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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
2 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
El V Encuentro Sud-Americano <strong>de</strong> Colisiones Inelásticas en la Materia es<br />
la continuación <strong>de</strong> los encuentros realizados en Gramado, Brasil, el 2002, en Viña<br />
<strong>de</strong>l Mar, Chile, el 2004, en Buenos Aires, Argentina, el 2006 y en Río <strong>de</strong> Janeiro,<br />
Brasil el 2008.<br />
El objetivo principal <strong>de</strong> estos encuentros Sud Americanos es fomentar el<br />
intercambio científico regional, para propiciar activida<strong>de</strong>s <strong>de</strong> cooperación entre<br />
Argentina, Brasil y Chile. Adicionalmente, estos encuentros ofrecen a los<br />
alumnos <strong>de</strong> posgrado entrar en contacto con investigadores <strong>de</strong>l área <strong>de</strong> colisiones<br />
inelásticas y sus aplicaciones y generar intercambio y colaboraciones mutuas.<br />
El programa consistirá en presentaciones orales y paneles, disponiéndose <strong>de</strong><br />
tiempo suficiente para discusiones informales en torno a los temas presentados.<br />
Los idiomas oficiales <strong>de</strong> la reunión serán el español y el portugués.<br />
Áreas <strong>de</strong> Interés: Esta reunión cubrirá las diferentes áreas relacionadas con el<br />
estudio básico <strong>de</strong> las interacciones <strong>de</strong> iones con sólidos, superficies y gases, y sus<br />
aplicaciones. <strong>Técnica</strong>s espectroscópicas (TOF, PIXE, RBS, ERDA, NRA,<br />
FEEL), caracterización <strong>de</strong> materiales implantados, interacción <strong>de</strong> iones con<br />
átomos, moléculas y nanoestructuras.<br />
3 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Comité Asesor Científico<br />
Moni Behar<br />
Pedro L. Gran<strong>de</strong><br />
Nestor Arista<br />
Jorge Miraglia<br />
Roberto Rivarola<br />
Nelson V. Castro Faría<br />
Eduardo Montenegro<br />
Enio F. Da Silveira<br />
Jorge E. Valdés<br />
Coordinadores<br />
Moni Behar<br />
Pedro L. Gran<strong>de</strong><br />
Jorge Miraglia<br />
Nestor Arista<br />
Jorge E. Valdés<br />
Comité Organizador Local<br />
Carlos Celedón<br />
Shimrit Elimelech<br />
Emilio Figueroa<br />
Joaquín Díaz <strong>de</strong> Valdés<br />
Patricio Vargas C.<br />
Jorge E. Valdés<br />
Secretaría: Marcela Aguirre W.<br />
Teléfono: +56 32 2654142/4625<br />
Av. España 1680, Casilla 110-V,<br />
Valparaíso, Chile<br />
4 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Contenido<br />
Comité Asesor Científico ..................................................................................4<br />
Coordinadores................................................................................................4<br />
Comité Organizador Local ................................................................................4<br />
Programa.................................................................................... 9<br />
Contribuciones ......................................................................... 13<br />
Ab-Initio Sturmian method for three-body quantum mechanical problems: Atomic<br />
and molecular bound states ........................................................................... 15<br />
Aplicações <strong>de</strong> PIXE na UFRGS ......................................................................... 17<br />
Atomistic simulations of swift ion bombardment ................................................ 18<br />
Caracterização <strong>de</strong> nanoestruturas usando a técnica MEIS ................................... 19<br />
Chemical Characterization of Fish-Otoliths using Micro-PIXE................................ 20<br />
Depth profiling of thin films using Coulomb explosion......................................... 22<br />
Discrepancias post-prior y apantallamiento electrónico dinámico.......................... 23<br />
Electron transfer processes in particle surface interactions.................................. 25<br />
Endohedrally confined atoms in Fullerenes: He (and the time capsule) ................. 26<br />
Estudio teórico-experimental <strong>de</strong> efectos <strong>de</strong> orientación en procesos <strong>de</strong> ionización en<br />
colisiones H + +He ......................................................................................... 28<br />
Estudo da ionização direta <strong>de</strong> átomos <strong>de</strong> neônio por impacto <strong>de</strong> íons <strong>de</strong> boro com<br />
energias <strong>de</strong> 1-4 MeV ..................................................................................... 30<br />
Excitación <strong>de</strong> excitones en colisiones <strong>de</strong> iones con Cristales <strong>de</strong> FLi: un mo<strong>de</strong>lo tipocebolla<br />
.................................................................................................... 31<br />
Fast atom diffraction from metallic surfaces...................................................... 32<br />
Influence of light-ion irradiation on the ion track etching of polycarbonate ............ 34<br />
Interacción <strong>de</strong> haces <strong>de</strong> protones con materiales <strong>de</strong> interés biológico ................... 36<br />
Interaction Dynamics of Clusters In Intense Laser Fields .................................... 38<br />
Ionización múltiple <strong>de</strong> Ne, Ar, Kr y Xe <strong>de</strong>bido al impacto <strong>de</strong> iones H+ y He+ ......... 39<br />
Ionization pattern in the region of the Bragg peak ............................................. 41<br />
Laboratorio Tan<strong>de</strong>m <strong>de</strong> 1.7MV <strong>de</strong>l Centro Atómico Bariloche ............................... 42<br />
LPA stopping power of swift ions in solids. Mo<strong>de</strong>ling the inhomogeneous electron gas<br />
.................................................................................................... 44<br />
Manipulation of magnetic and electronic properties of Ga 1-x Mn x As by ion beam<br />
irradiation.................................................................................................... 46<br />
Medidas da distribuição <strong>de</strong> energia <strong>de</strong> moléculas e fragmentos moleculares por<br />
espectroscopia <strong>de</strong> tempo <strong>de</strong> vôo com extração retardada ................................... 47<br />
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Perda <strong>de</strong> energia <strong>de</strong> elétrons em água ............................................................. 48<br />
Plasmon excitation in single walled carbon nanotubes by charged particles ........... 49<br />
Processos <strong>de</strong> Troca <strong>de</strong> Carga na Ionização Múltipla <strong>de</strong> Gases Nobres por Íons <strong>de</strong> C 3+ .<br />
.................................................................................................... 50<br />
Prospects for a new synchrotron light source in Brazil ........................................ 51<br />
Quantum-mechanical and classical cross sections for ionization and capture induced<br />
by light ions on DNA and RNA nucleobases ....................................................... 52<br />
Secondary Ions emission from Alkanethiol-SAMs due to highly charged ions<br />
bombardment .............................................................................................. 54<br />
Structural characterization of Pb nanoislands in SiO 2 /Si interface synthe-sized by ion<br />
implantation through MEIS analysis................................................................. 55<br />
Supression of binary and recoil peaks in ionization of H 2 by electron impact .......... 57<br />
The role of electronic excitations in the energy loss of hydrogen clusters in dielectric<br />
and metallic materials ................................................................................... 59<br />
Contribuciones - Paneles ........................................................ 61<br />
P1 Electron emission by grazing scattering from Be(0001)......................... 65<br />
P2 Monte Carlo simulation for proton track structure in biological matter ..... 67<br />
P3 Multiple differential cross sections for the ionization from the 1B1 orbital of<br />
liquid water molecule by fast electron impact.................................................... 68<br />
P4 I<strong>de</strong>ntificação dos caminhos <strong>de</strong> fragmentação da molécula <strong>de</strong> CHClF 2<br />
quando ionizada por elétrons.......................................................................... 70<br />
P5 Café Brasileiro: Estudo da Concentração Elementar Utilizando Feixes<br />
Iônicos .................................................................................................... 72<br />
P6 Coherencia y localización parcial en emisión electrónica simple <strong>de</strong><br />
moléculas diatómicas moléculas biatómicas ...................................................... 73<br />
P7 Estados selectivos <strong>de</strong> captura <strong>de</strong> electrones en colisiones <strong>de</strong> 3 He 2+ +He a<br />
energías intermedias <strong>de</strong> impacto aplicando la técnica COLTRIMS ......................... 75<br />
P8 Estudio <strong>de</strong> colisiones con proyectiles neutros y cargados sobre blancos<br />
moleculares <strong>de</strong> H 2 a energías intermedias <strong>de</strong> impacto con la técnica COLTRIMS ..... 77<br />
P9 Doble Ionización <strong>de</strong> Helio por impacto <strong>de</strong> iones: Influencia <strong>de</strong> la Carga <strong>de</strong>l<br />
Proyectil .................................................................................................... 79<br />
P10 Lα, Lβ, and Lγ x-ray production cross sections of Sm, Dy, Ho, and Tm by<br />
electron impact. Distorted-wave calculations vs experiment ................................ 80<br />
P11 Estudio <strong>de</strong> po<strong>de</strong>r <strong>de</strong> frenado <strong>de</strong> partículas α en películas <strong>de</strong>lgadas <strong>de</strong> cobre<br />
en el intervalo <strong>de</strong> energía entre 1,0 a 2,0 MeV .................................................. 82<br />
P12 Ab-Initio Sturmian method for three-body quantum mechanical problems:<br />
Scattering states and ionizing collisions............................................................ 84<br />
P13 Ionización <strong>de</strong> hidrógeno atómico e iones moleculares H + 2 por pulsos láser .<br />
.................................................................................................... 85<br />
P14 Un mo<strong>de</strong>lo <strong>de</strong> onda distorsionada para ionización electrónica en colisiones<br />
entre iones vestidos y blancos atómicos........................................................... 87<br />
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P15 Canalización cuasiplanar <strong>de</strong> protones energéticos en inci<strong>de</strong>ncia normal<br />
sobre nanotubos <strong>de</strong> carbono <strong>de</strong> pared múltiple ................................................. 89<br />
P16 Bulk plasmon excitation in grazing inci<strong>de</strong>nce ionmetal surface collisions.. 91<br />
P17 Distribuciones <strong>de</strong> Scattering Múltiple y Efectos Angulares en la Pérdida <strong>de</strong><br />
energía <strong>de</strong> Protones y Deuterones en Láminas Delgadas <strong>de</strong> Carbono Amorfo ......... 92<br />
P18 Stopping power y Straggling <strong>de</strong> protones en Pd................................... 93<br />
P19 Energy Loss of slow Hydrogen and Helium ions in channeling conditions in<br />
Au single crystal ........................................................................................... 94<br />
P20 Pérdida <strong>de</strong> energía <strong>de</strong> protones en láminas <strong>de</strong>lgadas <strong>de</strong> Carbono amorfo 95<br />
P21 Energy losses of H and F ions in grazing scattering on a missing row<br />
reconstructed Au(110) surface........................................................................ 97<br />
P22 Inverse photoemission espectroscopy on graphene .............................. 99<br />
P23 Elemental analysis of the Chaitén volcano ash 2008-2009 eruptions..... 100<br />
P24 Múltipla ionização <strong>de</strong> Neônio em coincidência com íons <strong>de</strong> B 2+ no regime <strong>de</strong><br />
energia <strong>de</strong> poucos MeV................................................................................ 102<br />
Índice <strong>de</strong> autores ................................................................... 103<br />
Corres electrónicos participantes .......................................... 105<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
8 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Programa<br />
Inicio MARTES - 30 <strong>de</strong> noviembre EXPOSITOR MODERADOR<br />
8:30 INSCRIPCIONES<br />
9:30 Atomistic simulations of swift ion bombardment Eduardo Bringa (Argentina)<br />
10:05<br />
10:30<br />
The role of electronic excitations in the energy loss of<br />
hydrogen clusters in dielectric and metallic materials<br />
Ionización múltiple <strong>de</strong> Ne, Ar, Kr y Xe <strong>de</strong>bido al impacto <strong>de</strong><br />
iones H+ y He+<br />
Samir. M. Shubeita (Brasil)<br />
Claudia Montanari (Argentina)<br />
10:55 C A F E<br />
11:10 Prospects for a new synchrotron light source in Brazil Gustavo <strong>de</strong> Azevedo (Brasil)<br />
Nestor Arista<br />
11:45<br />
12:10<br />
12:35<br />
Excitación <strong>de</strong> excitones en colisiones <strong>de</strong> iones con<br />
Cristales <strong>de</strong> FLi: un mo<strong>de</strong>lo tipo-cebolla<br />
Medidas da distribuição <strong>de</strong> energia <strong>de</strong> moléculas e<br />
fragmentos moleculares por espectroscopia <strong>de</strong> tempo <strong>de</strong><br />
vôo com extração retardada.<br />
Endohedrally confined atoms in Fullerenes: He (and the<br />
time capsule)<br />
Jorge E. Miraglia (Argentina)<br />
Natalia Ferreira (Brasil)<br />
Darío Mitnik (Argentina)<br />
13:00 ALMUERZO - FOTO<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Inicio MARTES - 30 <strong>de</strong> noviembre EXPOSITOR MODERADOR<br />
15:00 Interaction dynamics of clusters in intense laser fields Dominique Vernhet (France)<br />
15:35 Aplicações <strong>de</strong> PIXE na UFRGS Liana A. Boufleur (Brasil)<br />
16:00<br />
Quantum-mechanical and classical cross sections for<br />
ionization and capture induced by light ions on DNA and<br />
RNA nucleobases<br />
16:25 C A F E<br />
Christophe Champion (France)<br />
16:40<br />
Laboratorio Tan<strong>de</strong>m <strong>de</strong> 1.7MV <strong>de</strong>l Centro Atómico<br />
Bariloche<br />
Sergio Suárez (Argentina)<br />
Geraldo Sigaud<br />
17:15 Caracterização <strong>de</strong> nanoestruturas usando a técnica MEIS Mauricio A. Sortica (Brasil)<br />
17:40<br />
18:05<br />
LPA stopping power of swift ions in solids. Mo<strong>de</strong>ling the<br />
inhomogeneous electron gas<br />
Structural characterization of Pb nanoislands in SiO2/Si<br />
interface synthe-sized by ion implantation through MEIS<br />
analysis<br />
José María Fernán<strong>de</strong>z-Varea<br />
(España)<br />
Dario Sanchez (Brasil)<br />
20:00 CENA DE CAMARADERIA<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Inicio MIÉRCOLES - 1 Diciembre EXPOSITOR Mo<strong>de</strong>rador<br />
9:30<br />
Interacción <strong>de</strong> haces <strong>de</strong> protones con materiales <strong>de</strong><br />
interés biológico<br />
Rafael García-Molina (España)<br />
10:05 Perda <strong>de</strong> energia <strong>de</strong> elétrons em água André C. Tavares (Brasil)<br />
10:30 ECOS - CONICYT Dominique Vernhet (France)<br />
10:55 C A F E<br />
11:10<br />
11:45<br />
12:10<br />
12:35<br />
Electron transfer processes in particle surface<br />
interactions.<br />
Discrepancias post-prior y apantallamiento electrónico<br />
dinámico<br />
Processos <strong>de</strong> Troca <strong>de</strong> Carga na Ionização Múltipla <strong>de</strong><br />
Gases Nobres por Íons <strong>de</strong> C3+<br />
Supression of binary and recoil peaks in ionization of H2<br />
by electron impact<br />
13:00 ALMUERZO<br />
Vladimir Esaulov (France)<br />
Roberto D. Rivarola (Argentina)<br />
Geraldo Monteiro Sigaud (Brasil)<br />
Omar A . Fojón (Argentina)<br />
Eduardo Bringa<br />
15:00<br />
Secondary Ions emission from Alkanethiol-SAMs due to<br />
highly charged ions bombardment<br />
Marcos Flores (Chile)<br />
15:35<br />
16:00<br />
Chemical Characterization of Fish-Otoliths using Micro-<br />
PIXE<br />
Ab-Initio Sturmian method for three-body quantum<br />
mechanical problems: Atomic and molecular bound states<br />
16:25 C A F E<br />
16:40<br />
Influence of light-ion irradiation on the ion track etching<br />
of polycarbonate<br />
Elis Moura Stori (Brasil)<br />
Juan Martin Randazzo (Argentina)<br />
Claudia Telles <strong>de</strong> Souza (Brasil)<br />
Eduardo Montenegro<br />
17:05<br />
Plasmon excitation in single walled carbon nanotubes by<br />
charged particles<br />
Silvina Segui (Argentina)<br />
17:30 SESIÓN DE PANELES<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Inicio JUEVES - 2 diciembre EXPOSITOR Mo<strong>de</strong>rador<br />
9:30 Ionization pattern in the region of the Bragg peak Eduardo Montenegro (Brasil)<br />
10:05 Fast atom diffraction from metallic surfaces María Silvia Gravielle (Argentina)<br />
10:30 Depth profiling of thin films using Coulomb explosion Pedro L. Gran<strong>de</strong> (Brasil)<br />
10:55 C A F E<br />
11:10<br />
Estudo da ionização direta <strong>de</strong> átomos <strong>de</strong> neônio por<br />
impacto <strong>de</strong> íons <strong>de</strong> boro com energias <strong>de</strong> 1-4 MeV<br />
Hugo M. R. <strong>de</strong> Luna (Brasil)<br />
Roberto Rivarola<br />
11:35<br />
Estudio teórico-experimental <strong>de</strong> efectos <strong>de</strong> orientación en<br />
procesos <strong>de</strong> ionización en colisiones H+ +He<br />
Juan Fiol (Argentina)<br />
12:00<br />
Manipulation of magnetic and electronic properties of Ga1<br />
- xMnxAs by ion beam irradiation<br />
Marcelo M. Sant’Anna (Brasil)<br />
12:25 CLAUSURA<br />
13:05 ALMUERZO<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Contribuciones<br />
13 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
14 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Ab-Initio Sturmian method for three-body quantum mechanical problems:<br />
Atomic and molecular bound states<br />
J. M. Randazzo 1 , 5 , A. L. Frapiccini 1 , 5 ,<br />
G. Gasaneo 2 , 5 , F. D. Colavecchia 1 , 5 , D. M. Mitnik 3 , 5 and L. U. Ancarani 4<br />
1 División <strong>de</strong> Colisiones Atómicas, Centro atómico Bariloche, San Carlos <strong>de</strong> Bariloche, Río Negro, Argentina.<br />
2 Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> Nacional <strong>de</strong>l Sur, Bahía Blanca, Buenos Aires, Argentina<br />
3 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio and <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> Ciencias Exactas y Naturales,<br />
<strong>Universidad</strong> <strong>de</strong> Buenos Aires C.C. 67, Suc. 28, (C1428EGA) Buenos Aires, Argentina.<br />
4 Laboratoire <strong>de</strong> Physique Moléculaire et <strong>de</strong>s Collisions,Université Paul Verlaine-Metz, 57078 Metz, France.<br />
5 Consejo Nacional <strong>de</strong> Investigaciones Científicas y <strong>Técnica</strong>s (CONICET).<br />
email address corresponding author: randazzo@cab.cnea.gov.ar<br />
In this work we review a recently introduced<br />
methodology to solve the<br />
Schrödinger equation of three particles. We<br />
assume that the particles interact through<br />
potentials <strong>de</strong>pending only on the distances<br />
between them. The most general Schrödinger<br />
equation we will consi<strong>de</strong>r reads:<br />
together with the boundary conditions:<br />
and<br />
Where U 1 , U 2 and U 12 can be any well behaved<br />
atomic potentials. We also assume that<br />
U 12 admits a simple partial wave expansion,<br />
such as Coulomb, Yukawa, armonic potentials,<br />
etc.<br />
Because of the symmetries of the Eq.<br />
(1), the wave function can be evaluated separately<br />
for each L, M, S and Π (total angular<br />
momentum, its projection along the z axis,<br />
the spin symmetry and parity, respectively).<br />
We then propose a partial wave expansion in<br />
terms of the bi-spherical harmonics, and obtain<br />
a coupled set of two-dimensional equations<br />
in the radial coordinates r 1 and r 2 .<br />
The set of coupled equations is solved<br />
by means of a Sturmian expansion (one<br />
Sturmian set for each coordinate)[1]. The<br />
Generalized Sturmian functions are solutions<br />
of the Sturm-Liouville equation:<br />
where V is a short range generating potential,<br />
β is the eigenvalue and E is consi<strong>de</strong>red<br />
as a parameter. Constructing the basis in this<br />
way enables us to set boundary conditions of<br />
the complete problem in each Sturmian <strong>de</strong>pending<br />
on coordinates r 1 and r 2 : Kato cusp<br />
conditions and Coulomb exponentially <strong>de</strong>caying<br />
behaviour for negative energies, or Coulomb<br />
outgoing wave conditions for positive<br />
ones[2].<br />
In this work we will show some results of the<br />
application of the Sturmian expansion to the<br />
solution of equation (1) for a variety of three<br />
body boun<strong>de</strong>d atomic and molecular systems<br />
and mo<strong>de</strong>ls. We choose here using negative<br />
energy Sturmian functions, and compute<br />
ground as well as the different manifolds of<br />
excited states. We also analyze different<br />
choices for the generating potential to<br />
achieve a high <strong>de</strong>gree of accuracy in the en-<br />
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ergies of the states. For an optimal choice of<br />
the potential, with 35 Sturmians per electron,<br />
we found E=-2.903 712 820 a.u. for the He<br />
ground state, (reference value: -2.903 724<br />
377 a.u. [3]).<br />
Acknowledgements<br />
This work has been supported by PICT 08/0934<br />
of ANPCYT (Argentina), PIP 200901/552 of<br />
Conicet (Argentina), and PGI Grant No.<br />
24/F049, <strong>Universidad</strong> Nacional <strong>de</strong>l Sur (Argentina).<br />
References<br />
[1] J. M. Randazzo, L. U. Ancarani, G. Gasaneo,<br />
A. L. Frapiccini, and F. D. Colavecchia, Phys.<br />
Rev. A 81, 042520 (2010).<br />
[2] J. M. Randazzo, A.L. Frapiccini, F. D.<br />
Colavecchia, and G. Gasaneo, Phys. Rev. A<br />
79, 022507 (2009).<br />
[3] G.W.F. Drake, Handbook of Atomic,<br />
Molecular, and Optical Physics, (Springer,<br />
Hei<strong>de</strong>lberg/New York, 2005).<br />
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Aplicações <strong>de</strong> PIXE na UFRGS<br />
L. A. Boufleur 1 , C. E. Iochims dos Santos 1 , R. Debastiani 1 , L. Amaral 1 , J. F. Dias 1<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Porto Alegre, Brasil<br />
Autor correspon<strong>de</strong>nte: carlaiochims@yahoo.com.br<br />
A <strong>de</strong>terminação <strong>de</strong> elementos<br />
químicos em alimentos e no meio ambiente e<br />
o conhecimento da interação <strong>de</strong> tais<br />
elementos com os organismos vivos são<br />
indispensáveis para controle <strong>de</strong> qualida<strong>de</strong> e<br />
toxicida<strong>de</strong>, tanto na produção <strong>de</strong> alimentos<br />
quanto na contaminação ambiental e<br />
exposição ocupacional.<br />
Neste contexto, o grupo PIXE do<br />
Laboratório <strong>de</strong> Implantação Iônica do<br />
Instituto <strong>de</strong> <strong>Física</strong> da Universida<strong>de</strong> Fe<strong>de</strong>ral do<br />
Rio Gran<strong>de</strong> do Sul (UFRGS) realiza diversos<br />
trabalhos <strong>de</strong> <strong>de</strong>terminação da composição<br />
elementar em alimentos, bebidas e amostras<br />
biológicas em geral.<br />
Como trabalho pioneiro no Brasil<br />
com a técnica PIXE, foi realizado o estudo da<br />
composição elementar do vinho varietal<br />
Cabernet Sauvignon proce<strong>de</strong>nte do Vale dos<br />
Vinhedos e outras três regiões do estado [1].<br />
Dentre outros resultados, diferenças<br />
nos conteúdos elementares <strong>de</strong> potássio e<br />
fósforo entre vinhos produzidos em tal região<br />
revelam a influência do cultivo da uva e do<br />
processamento da bebida, próprios <strong>de</strong> cada<br />
vinícola.<br />
Outro exemplo diz respeito à<br />
<strong>de</strong>terminação <strong>de</strong> ferro, cobre, chumbo, zinco,<br />
alumínio, <strong>de</strong>ntre outros, no fígado <strong>de</strong><br />
morcegos <strong>de</strong> uma região mineradora <strong>de</strong> <strong>Santa</strong><br />
Catarina, e respectivos danos no DNA [2].<br />
Para uma das espécies estudadas, foi<br />
observado um maior índice <strong>de</strong> danos no DNA<br />
dos habitantes da região mineradora<br />
comparado aos da região controle,<br />
possivelmente <strong>de</strong>vido à maior exposição ao<br />
ferro e ao cobre na área <strong>de</strong> mineração.<br />
Além <strong>de</strong>stes, outros trabalhos estão<br />
em andamento ou em fase <strong>de</strong> conclusão,<br />
como o estudo da composição elementar <strong>de</strong><br />
alimentos enlatados, da cerveja e do café; a<br />
investigação do papel <strong>de</strong> certos elementos em<br />
processos como os <strong>de</strong> aprendizagem,<br />
aquisição e consolidação da memória e a<br />
<strong>de</strong>terminação da espessura <strong>de</strong> filmes finos por<br />
MEIS, PIXE e NRP.<br />
Referências<br />
[1] C. E. Iochims dos Santos et al, Food<br />
Chemistry 121, 244 (2010).<br />
Figura 1: Espectro PIXE típico <strong>de</strong> um vinho<br />
Cabernet Sauvignon (safra 2002) como função da<br />
energia do raio X (em KeV).<br />
[2] Zocche et al, Environmental Research<br />
110, 684 (2010).<br />
17 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Atomistic simulations of swift ion bombardment<br />
Eduardo M. Bringa 1<br />
1 CONICET & Instituto <strong>de</strong> Ciencias Básicas, <strong>Universidad</strong> Nacional <strong>de</strong> Cuyo, Mendoza 5500, Argentina<br />
email address corresponding author: ebringa@yahoo.com<br />
Atomistic simulations are often used<br />
to study the bombardment of ions in the regime<br />
where elastic collisions dominate, but<br />
they rarely mo<strong>de</strong>l bombardment when electronic<br />
effects dominate energy <strong>de</strong>position in<br />
the target. There are several mo<strong>de</strong>ls to inclu<strong>de</strong><br />
these electronic effects within classic<br />
molecular dynamics (MD) simulations like<br />
Coulomb explosions, “thermal spikes”, and<br />
etcetera. MD simulations follow the evolution<br />
of a system of atoms interacting trough<br />
some empirical potential. Using current parallel<br />
computers millions of atoms can be<br />
followed during tens of picoseconds. Such<br />
systems are large enough and can be studied<br />
long enough to account for the early stages<br />
of radiation damage. Later stages have to be<br />
studied with other techniques, like kinetic<br />
Monte Carlo or rate theory.<br />
Ion tracks [1], surface craters [2] or<br />
hillocks, electronic sputtering [3], and other<br />
radiation damage indicators can be predicted<br />
in this way. Examples from materials<br />
science, surface physics, and astrophysics<br />
will be shown to illustrate that these mo<strong>de</strong>ls<br />
are relatively simple, but provi<strong>de</strong> a reasonable<br />
<strong>de</strong>scription of experimental results when<br />
electronic stopping power cannot be neglected.<br />
Future directions to <strong>de</strong>scribe electronic<br />
effects in atomistic simulations will<br />
also be discussed.<br />
This work has been carried out in<br />
collaboration with several people, including<br />
D. Schwen, D. Farkas, J. Monk, A.<br />
Caro, J. Rodriguez-Nieva, T. Cassidy,<br />
R.E. Johnson, R. Papaléo, M. Da Silva, C.<br />
Ruestes, and Nestor Arista.<br />
Figure 1. MD simulation of hillocks in tetrahedral<br />
amorphous carbon, showing increasing hillock<br />
height with increasing electronic stopping [4].<br />
References<br />
[1] R. Devanathana, P. Durhamb, J. Dua, L.R.<br />
Corrales and E.M. Bringa, Nuclear Instruments<br />
and Methods in Physics Research Section B 255,<br />
172 (2007).<br />
[2] E.M. Bringa, R.E. Johnson, R. M. Papaléo,<br />
Phys. Rev. B 65, 094113 (2002).<br />
[3] E.M. Bringa and R.E. Johnson, Phys. Rev.<br />
Lett. 88, 165501 (2002).<br />
[4] D. Schwen and E.M. Bringa, submitted<br />
(2010).<br />
18 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Caracterização <strong>de</strong> nanoestruturas usando a técnica MEIS<br />
M. A. Sortica 1 , P. L. Gran<strong>de</strong> 1 , C. Radtke 2 , G. Machado 3<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Porto Alegre-RS, Brasil<br />
2 Instituto <strong>de</strong> Química, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul,Porto Alegre-RS, Brasil<br />
3 Centro <strong>de</strong> Tecnologias Estratégica do Nor<strong>de</strong>ste, Recife-PE,, Brasil<br />
e-mail: sortica@if.ufrgs.br<br />
Espalhamento <strong>de</strong> íons com média<br />
energia (MEIS) é uma técnica analítica <strong>de</strong><br />
caracterização por feixe <strong>de</strong> íons, capaz <strong>de</strong><br />
<strong>de</strong>terminar quantitativamente composição<br />
elementar e perfil <strong>de</strong> profundida<strong>de</strong> com<br />
resolução subnanométrica. Isso torna o<br />
MEIS uma pon<strong>de</strong>rosa ferramenta para<br />
caracterização <strong>de</strong> nanoestruturas [1], com<br />
resolução para fazer perfilometria <strong>de</strong>ntro <strong>de</strong><br />
nanoestruturas com tamanhos abaixo <strong>de</strong> 5<br />
nm [2]. Para isso, <strong>de</strong>senvolvemos um<br />
software Monte Carlo para simulação e<br />
ajuste <strong>de</strong> espectros <strong>de</strong> MEIS [3], que leva<br />
em conta a forma geométrica, distribuição<br />
<strong>de</strong> tamanhos e <strong>de</strong>nsida<strong>de</strong> <strong>de</strong> nanoestru-turas.<br />
Nosso software (PowerMeis) tam-bém<br />
consi<strong>de</strong>ra a forma assimétrica da distribuição<br />
<strong>de</strong> perda <strong>de</strong> energia [4, 5].<br />
Nesse trabalho apresentamos 2<br />
estudos. O primeiro sistema se refere à<br />
interação entre nanopartículas esféricas <strong>de</strong><br />
ouro e um filme formado por multi-camadas<br />
<strong>de</strong> polieletrólitos fracos [6] (Figura 1).<br />
Figura 1. (a) Esquema da síntese das 20 bicamadas<br />
(LbL) usando PAH/PAA. Em <strong>de</strong>talhe uma<br />
representação <strong>de</strong> como se forma uma LbL. (b)<br />
Configuração esquemática <strong>de</strong> uma NP <strong>de</strong> ouro<br />
estabilizada com citrato, indicando que a carga<br />
superficial é negativa.<br />
A difusão ou adsorção <strong>de</strong> nano-partículas<br />
através do filme po<strong>de</strong> ser controlada<br />
modificando o pH dos polieletrólitos e da<br />
solução coloidal <strong>de</strong> nanoparticulas <strong>de</strong> ouro,<br />
possibilitando a formação <strong>de</strong> uma ou duas<br />
camadas <strong>de</strong> NPs na superfície ou a<br />
penetração <strong>de</strong> NPs com <strong>de</strong>terminados<br />
tamanhos. Nesse estudo, usamos MEIS para<br />
mo<strong>de</strong>lar a interface entre ouro e filme<br />
(Figura 2). O segundo sistema tem como<br />
objetivo a caracterização da estrutura coreshell<br />
<strong>de</strong> nanopartículas esféricas <strong>de</strong> CdSe,<br />
recobertas por ZnS, <strong>de</strong>positadas sobre óxido<br />
<strong>de</strong> silício.<br />
Figura 2. Sequência <strong>de</strong> espectros 2D (energy/ angle)<br />
<strong>de</strong> MEIS (a, b, c, d) e 1D, para um ângulo <strong>de</strong><br />
espalhamento <strong>de</strong> 120 o , (e, f, g and h) para 4<br />
diferentes sistemas LbL. (i, j, l, m) correspon<strong>de</strong>m às<br />
configurações <strong>de</strong> NPs que melhor ajustam o espectro<br />
<strong>de</strong> MEIS.<br />
Referências<br />
[1] J. P. Stoquert, T. Szörenyi, Phys. Rev B 67<br />
(2002) 144108.<br />
[2] H. Matsumoto, K. Mitsuhara, A. Visikovskiy,<br />
T. Akita, N. Toshima, Y. Kido, Nucl. Instr. and<br />
Meth. in Phys. Res. B, (2010) DOI<br />
10.1016/j.nimb.2010.03.032 .<br />
[3] I. Konomi, S. Hyodo, T. Motohiro, Journal of<br />
Catalysis 192 (2000) 11-17.<br />
[4] P. L. Gran<strong>de</strong>, A. Hentz, R. P. Pezzi, I. J. R.<br />
Baumvol, G. Schiwietz, Nucl. Instr. and Meth. In<br />
Phys. Res. B 256 (2007) 92-96.<br />
[5] M. A. Sortica, P. L. Gran<strong>de</strong>, G. Machado, L.<br />
Miotti, Journal of Applied Physics 106 (2009)<br />
114320.<br />
[6] G. Decher, Science, 1997, 277, 1232-1237.<br />
19 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Chemical Characterization of Fish-Otoliths using Micro-PIXE<br />
Stori, E. M. 1 , Dias, J. F. 1 , Favero, J. M. 2 , Dias, J. F. 2<br />
1 Laboratório <strong>de</strong> Implantação Iônica – Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Av. Bento<br />
Gonçalves 9500, Porto Alegre, RS , Brasil<br />
2 Instituto <strong>de</strong> Oceanografia – Universida<strong>de</strong> Estadual <strong>de</strong> São Paulo – São Paulo, SP, Brasil<br />
email address corresponding author: elistori@gmail.com<br />
Fishes contain a group of three pairs of<br />
bone structures in their ear that are responsible<br />
for hearing and equilibrium. These structures<br />
grow in layers that look like rings if<br />
sectioned (figure 1). [1]<br />
of interest and its position in the otolith.<br />
[5][6]<br />
The knowledge of the trace elements<br />
present in different rings would allow to establish<br />
a relation between different places the<br />
fish have lived and the stages of its life.<br />
Figure 2 shows calcium maps of a juvenile<br />
fish otolith, in which can be observed<br />
the growth rings through the difference of<br />
intensity of the calcium signal.<br />
Figure 1. Sectioned otolith showing growth rings [2]<br />
There are very well <strong>de</strong>veloped studies<br />
that relate the rings in the otoliths with the<br />
fishes’ age. While in adult’s otoliths the rings<br />
may represent years of age, in juvenile fishes<br />
and larvae the rings represent days. [1]<br />
Moreover, the otoliths may give information<br />
of fish migration pattern or their origin<br />
by <strong>de</strong>termining the trace elements contained<br />
in them. [3][4]<br />
The micro-PIXE technique (micro-<br />
Particle Induced X-Ray Emission) is not<br />
regularly used to <strong>de</strong>termine trace elements in<br />
otoliths. Its advantages inclu<strong>de</strong> the non<strong>de</strong>structive<br />
character of the technique, and<br />
the possibility of a spacial characterization of<br />
the elements, enabling a more accurate analysis<br />
of the relation between the trace element<br />
(a)<br />
(b)<br />
Figure 2. Calcium maps of a juvenile fish otolith (a)<br />
the entire otolith and (b) a more <strong>de</strong>tailed map of the<br />
central region of the otolith.<br />
20 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
References<br />
[1] STEVENSON, D.K. and S.E. CAMPANA<br />
[ed]. 1992. Otolith microstructure examination<br />
and analysis. Can. Spec. Publ. Fish. Aquat. Sci.<br />
117: 130 pp<br />
[2] Tennessee Wildlife Resources Agency website:<br />
http://www.tnfish.org/AgeGrowth_TWRA/TWR<br />
A_FishAgeGrowth.htm<br />
[3] Bradbury, I. R., Campana, S. E., and<br />
Bentzen, P. 2008. Otolith elemental composition<br />
and adult tagging reveal spawning site fi<strong>de</strong>lity<br />
and estuarine <strong>de</strong>pen<strong>de</strong>ncy in rainbow smelt.<br />
Mar. Ecol. Prog. Ser. 368:255-268.<br />
[4] CAMPANA, S. E., VALENTIN, A., SÉVI-<br />
GNY, J.-M., and POWER, D. 2007. Tracking<br />
seasonal migrations of redfish (Sebastes spp.) in<br />
and around the Gulf of St. Lawrence using otolith<br />
elemental fingerprints. Can. J. Fish. Aquat.<br />
Sci. 64:6-18.<br />
[5] Johansson, S., Campbell, K. M., Particle-<br />
Induced X-ray Emission Spectrometry (PIXE),<br />
John Wiley & Sons, Inc., New York (1995)<br />
[6] Grime, G. W. and Watt, F., Beam Optics of<br />
Quadrupole Probe-forming Systems, Adam<br />
Higler Ltd., Bristol (1983)<br />
21 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Depth profiling of thin films using Coulomb explosion<br />
S. M. Shubeita 1 , P. L. Gran<strong>de</strong> 1 and J. F. Dias 1<br />
1 Instituto <strong>de</strong> <strong>Física</strong> da Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Porto Alegre, RS, Brazil<br />
e-mail address corresponding author: gran<strong>de</strong>@if.ufrgs.br<br />
Depth profiling of heavy elements in<br />
thin films can be performed by backscattering<br />
spectrometry. In this well established<br />
technique the <strong>de</strong>pth is given in units of<br />
length assuming the knowledge of the <strong>de</strong>nsity<br />
of the target. Otherwise “<strong>de</strong>pth” stands as<br />
an abbreviation for the number of atoms per<br />
unit area (<strong>de</strong>nsity) over the distance traversed<br />
(length) in the target [1]. A method to<br />
<strong>de</strong>termine the absolute <strong>de</strong>pth without the<br />
knowledge of the <strong>de</strong>nsity is useful since the<br />
<strong>de</strong>nsity is a physical quantity that can have<br />
different values for the same material.<br />
In this work we explore the Coulomb<br />
explosion occurring when energetic H 2<br />
+<br />
ionic clusters interact with thin layers of<br />
dielectric materials (LaScO 3 , HfO 2 and LaAlO<br />
3, thickness < 100 Å; and Si 3 15 N 4 and<br />
Al 2 O 3 , hundreds of Å). The molecules dissociate<br />
after passing the first monolayer and<br />
get stripped of all their electrons. The moving<br />
ionic fragments repel each other via mutual<br />
quasi Coulomb forces and excite the<br />
electronic medium coherently. The Coulomb<br />
explosion leads to a broa<strong>de</strong>ning of the energy-loss<br />
distribution of the ionic fragments,<br />
and can be evaluated through an additional<br />
energy-loss straggling.<br />
The information obtained by Coulomb<br />
explosion of H 2 + clusters in this approach<br />
can provi<strong>de</strong> the dwell time of the<br />
ionic fragments in thin layers after the breakup.<br />
In this way, the Coulomb explosion can<br />
work as a clock where the start is given by<br />
the electron striping and the stop by the<br />
backscattering. Thus the <strong>de</strong>termination of<br />
the absolute thickness of the thin films based<br />
in the dwell time (fig. 1) can be achieved.<br />
Figure 1. The experimental results of Coulomb explosion<br />
for HfO 2 as a function of the <strong>de</strong>pth traversed<br />
in comparison with calculations consi<strong>de</strong>ring<br />
screened and non-screened Coulomb potentials.<br />
For this purpose, high energy resolution<br />
backscattering experiments (MEIS: Medium<br />
Energy Ion Scattering) were carried<br />
out as a function of the incoming projectile<br />
energy, covering an energy range between<br />
100 and 200 keV/nucleon. Also, NRP (Nuclear<br />
Reaction Profiling) experiments were<br />
carried out on Si 3 15 N 4 ( 15 N(p,αγ) 12 C at 429<br />
keV/nucleon) and Al 2 O 3 ( 27 Al(p,γ) 28 Si at<br />
992 keV/nucleon) targets.<br />
The results obtained are compared<br />
with theoretical calculations and show the<br />
potentiality of a Coulomb explosion profiling<br />
technique.<br />
References<br />
[1] W. -K. Chu, J. W. Mayer, M. A. Nicolet,<br />
Backscattering Spectrometry (New York: <strong>Aca</strong><strong>de</strong>mic<br />
Press) (1978).<br />
22 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
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23 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
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24 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Electron transfer processes in particle surface interactions.<br />
Vladimir A. Esaulov<br />
Institut <strong>de</strong>s Sciences Moleculaires d’Orsay<br />
CNRS and Université Paris Sud, Orsay 91405, FRANCE<br />
vladimir.esaulov@u-psud.fr<br />
Electron transfer processes play an<br />
important role in adsorption and reactions at<br />
surfaces. Usual surface science experiments <strong>de</strong>al<br />
with the study of either the kinetics of<br />
adsorption/<strong>de</strong>sorption or with characterisation of<br />
adsorbates or products of reactions in situ.<br />
However the dynamics of the electron transfer<br />
process is usually not studied. I will discuss some<br />
experiments which allow us to obtain this<br />
information by scattering of atoms or ions on a<br />
surface and monitoring the energy and charge<br />
state of the scattered particles. These experiments<br />
allow one to obtain <strong>de</strong>tailed information in<br />
controlled conditions through a<strong>de</strong>quate choices of<br />
initial energy and impact angles and a selection of<br />
final charge state, trajectory (scattering angle) and<br />
energy. Information on electron transfer<br />
probabilities can be obtained for site specific or<br />
surface averaged conditions, mimicking different<br />
approaches of a gas phase particle to a surface.<br />
This quantitative data can serve as a rigorous test<br />
of theoretical mo<strong>de</strong>ls.<br />
observed.<br />
Another example concerns neutralisation<br />
of Li+ ions on Ag and Au clusters supported on<br />
titania (TiO2). Experiments as a function of<br />
growth of clusters an increase in their size have<br />
revealed that much larger neutralisation [4] is<br />
observed on small clusters than on large clusters<br />
or bulk like film.<br />
References<br />
[1] M. Wiatrowski, L. Lavagnino, V.A.<br />
Esaulov Surface Science, Volume 601, 2007,<br />
L39-L43<br />
[2] A R Canário , T Kravchuk and V A Esaulov<br />
2006 New J. Phys. 8 227<br />
[3] M. Casagran<strong>de</strong>, S. Lacombe, L.<br />
Guillemot, V. A. Esaulov Surface Science,<br />
445, 2000, Pages L29-L35<br />
[4] Ana Rita Canário and V. A. Esaulov, J .<br />
Chem. Phys. 124, 224710 (2006)<br />
Our main interest over the last few years,<br />
has been a study of progressively more complex<br />
cases serving to illustrate effects related to<br />
“promotion” or “poisoning” of reactions in<br />
catalysis and also the size effects. I shall illustrate<br />
our approach for several cases involving a clean<br />
metal surface, a surface with adsorbates and a<br />
nanoscale metal film or cluster supported on a<br />
metal or an oxi<strong>de</strong>. Some of these cases are well<br />
un<strong>de</strong>rstood but for some substantial theoretical<br />
effort has yet to be ma<strong>de</strong>.<br />
As examples I will mention typical results<br />
on negative ion formation for the case of fluorine<br />
negative ion scattering and Li+ neutralisation.<br />
Both involve resonant transfer of electrons. In<br />
case of Li+ ion neutralisation on metals and thin<br />
films recent experiments [1,2] have revealed<br />
“anomalously“ large neutralisation, much larger<br />
than what could be expected in “standard”<br />
mo<strong>de</strong>ls.<br />
The effect of adding controlled amounts<br />
of reactive adsorbates on metals will be illustrated<br />
on the case of chlorine adsorption [3] , where<br />
large changes in electron transfer probabilities are<br />
25 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Endohedrally confined atoms in Fullerenes: He (and the time capsule)<br />
Dario Mitnik 1 , Juan Randazzo 2 , Flavio Colavecchia 2 , y Gustavo Gasaneo 3<br />
1 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio y Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Argentina<br />
2 Centro Atómico Bariloche, Río Negro, Argentina<br />
3 Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> Nacional <strong>de</strong>l Sur, Bahía Blanca, Argentina<br />
email address corresponding author: dmitnik@df.uba.ar<br />
One of the most fascinating features of<br />
the<br />
fullerene molecules [1] is that they are capable<br />
of<br />
enclosing atoms in their hollow interior,<br />
forming endohedrally confined atoms. Experimental<br />
efforts have ma<strong>de</strong> it possible to<br />
trap atoms insi<strong>de</strong> a fullerene in different<br />
ways. The particular mechanisms responsible<br />
for the insertion of the atom, vary from a<br />
“brute force" implantation, to a “window"<br />
mechanism, in which high temperatures and<br />
pressures can break one of the Carbon-<br />
Carbon bonds in the cage. Small molecules<br />
and atoms can pass through this temporary<br />
hole, forming a stable endohedrally confined<br />
compound.<br />
The properties of a Helium atom confined<br />
insi<strong>de</strong> an endohedral<br />
cavity, like a fullerene, are studied. The<br />
fullerene cavity is mo<strong>de</strong>led by a potential<br />
well and the strength of<br />
this potential is varied in or<strong>de</strong>r to un<strong>de</strong>rstand<br />
the collapse of<br />
different atomic wavefunctions into the<br />
fullerene cage.<br />
Three theoretical calculation methods have<br />
been <strong>de</strong>veloped: a relaxation method, a Sturmian<br />
basis method, and a variational method.<br />
The first two methods are nonperturbative.<br />
The three methods allow inclusion of full<br />
correlations among the two electrons.<br />
Results showing mirror collapse effects are<br />
presented for an<br />
S-wave mo<strong>de</strong>l, in which all the angular quantum<br />
numbers are set to zero. In this work [2] we<br />
showed how the confinement potential<br />
strength<br />
affects in different amounts the atomic levels<br />
of the confined atom.<br />
Figure 1. First three wavefunctions, 1s2 1S, 1sy1 1S,<br />
and 1sy1 3S for different potential <strong>de</strong>pths, around the<br />
first avoi<strong>de</strong>d crossing at U0=1,185 a.u..<br />
Around the regions <strong>de</strong>noted as crossings, it<br />
seems that the variation in the potential produces<br />
<strong>de</strong>generacies in energy,<br />
indicating that the levels can cross each to the<br />
other.<br />
A <strong>de</strong>tailed analysis that requires a very high<br />
<strong>de</strong>gree of precision<br />
shows that the energy levels do not cross<br />
each other,<br />
but rather come close and repel each other<br />
yielding to<br />
an avoi<strong>de</strong>d crossing.<br />
We analyzed the behaviour of the avoi<strong>de</strong>d<br />
crossing levels by using<br />
different information entropies, providing an<br />
efficient tool to estimate in a physically<br />
transparent manner the<br />
26 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
atomic transitions caused by a slowly varying<br />
perturbation.<br />
References<br />
[1] Kroto H.W. et al., Nature 318, 162 (1985).<br />
[2] Mitnik, et al., Phys. Rev. A 78, 062501<br />
(2008).<br />
27 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Estudio teórico-experimental <strong>de</strong> efectos <strong>de</strong> orientación en<br />
procesos <strong>de</strong> ionización en colisiones H + +He<br />
D. Fregenal 1,2 , R. O. Barrachina 1,2 , G. Bernardi 1,2 , P. Focke 1,2 , S. G. Suárez 1,2 , J. Fiol 1,2<br />
1 Centro Atómico Bariloche and Instituto Balseiro (Comisión Nacional <strong>de</strong> Energía Atómica y Univ.<br />
Nacional <strong>de</strong> Cuyo), 8400 S. C. <strong>de</strong> Bariloche, Río Negro, Argentina.<br />
2 Consejo Nacional <strong>de</strong> Investigaciones Científicas y <strong>Técnica</strong>s (CONICET), Argentina.<br />
Correo Electrónico: fiol@cab.cnea.gov.ar<br />
Resultados recientes tanto a nivel experimental<br />
como teórico han revelado anomalías<br />
en las secciones eficaces <strong>de</strong> ionización <strong>de</strong><br />
átomos y moléculas por impacto <strong>de</strong> positrones<br />
[1–5]. Las secciones eficaces múltiplemente<br />
diferenciales muestran un corrimiento <strong>de</strong>l<br />
pico <strong>de</strong> electrones capturados al continuo<br />
<strong>de</strong>l proyectil (ECC) respecto <strong>de</strong> la posición<br />
obtenida teóricamente [2, 4]. Cálculos realizados<br />
con el método <strong>de</strong> trayectorias clásicas <strong>de</strong><br />
Monte Carlo han relacionado este <strong>de</strong>splazamiento<br />
con un fuerte alineamiento <strong>de</strong>l par<br />
electrón-positrón en el estado final <strong>de</strong>l sistema<br />
[5].<br />
Estos resultados nos han motivado a<br />
investigar la existenca <strong>de</strong> efectos similares<br />
<strong>de</strong> alineamiento en procesos <strong>de</strong> ionización<br />
atómica por impacto <strong>de</strong> iones. En esta comunicación<br />
presentamos datos teóricos y experimentales<br />
<strong>de</strong> secciones eficaces diferenciales <strong>de</strong><br />
ionización en colisiones <strong>de</strong> H + +He para energías<br />
inci<strong>de</strong>ntes entre 20 y 50 keV/uma.<br />
El experimento consistió <strong>de</strong> mediciones<br />
<strong>de</strong>l ángulo y la energía <strong>de</strong> los electrones emitidos<br />
mediante un espectrómetro electrostático<br />
cilíndrico. Para cada energía inci<strong>de</strong>nte se han<br />
<strong>de</strong>terminado más <strong>de</strong> 1200 combinaciones <strong>de</strong><br />
ángulo y energía <strong>de</strong> los electrones emitidos en<br />
la región cercana a la cúspi<strong>de</strong> <strong>de</strong> ECC. Estas<br />
mediciones <strong>de</strong>talladas nos permiten representar<br />
gráficos tridimensionales <strong>de</strong> la distribución<br />
<strong>de</strong> velocida<strong>de</strong>s relativas <strong>de</strong>l electrón respecto<br />
al proyectil.<br />
Los resultados experimentales muestran<br />
un fenómeno <strong>de</strong> alineamiento tan acentuado<br />
como el observado con positrones. Este efecto<br />
se pue<strong>de</strong> observar en la figura 1, don<strong>de</strong> se representa<br />
la sección eficaz doblemente diferencial<br />
en la región <strong>de</strong> velocida<strong>de</strong>s electrónicas<br />
correspondiente al pico <strong>de</strong> ECC, para el caso<br />
<strong>de</strong> protones inci<strong>de</strong>ntes sobre He con energías<br />
<strong>de</strong> E = 50 keV/uma.<br />
v' ⊥ / v p<br />
0.05<br />
0<br />
v p = 1.414 a.u.<br />
-0.05<br />
-0.15 -0.1 -0.05 0 0.05 0.1<br />
v' || / v p<br />
Figura 1. Distribución <strong>de</strong> velocida<strong>de</strong>s <strong>de</strong>l electron<br />
emitido respecto al proyectil en colisiones H + +He<br />
a energía 50 keV/uma.<br />
El fenómeno <strong>de</strong> alineamiento es más pronunciado<br />
para energías <strong>de</strong> colisión más bajas. Para<br />
32 keV/uma la velocidad relativa electrónprotón<br />
está más concentrada hacia valores<br />
negativos que a 50 keV (figura 2).<br />
v' ⊥ / v p<br />
0.05<br />
0<br />
v p = 1.123 a.u.<br />
-0.05<br />
-0.15 -0.1 -0.05 0 0.05 0.1<br />
v' || / v p<br />
Figura 2. Distribución <strong>de</strong> velocida<strong>de</strong>s relativas<br />
electron-proyectil en la región <strong>de</strong> la cúspi<strong>de</strong> <strong>de</strong><br />
ECC para una energía inci<strong>de</strong>nte <strong>de</strong> 32 keV/uma.<br />
Este comportamiento es consistente con<br />
el observado tanto en mediciones previas en<br />
colisiones ión-átomo a energías <strong>de</strong> inci<strong>de</strong>ncia<br />
<strong>de</strong> 100 y 200 keV/uma [6] así como con resultados<br />
recientes en colisiones con positrones<br />
[1, 2]. Adicionalmente, nuestros cálculos <strong>de</strong><br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Trayectorias Clásicas <strong>de</strong> Monte Carlo reproducen<br />
este comportamiento, <strong>de</strong> manera similar<br />
al caso <strong>de</strong> impacto <strong>de</strong> positrones.<br />
Referencias<br />
[1] A. Kövér and G. Laricchia,<br />
Phys. Rev. Lett. 80, 5309 (1998).<br />
[2] A. Kövér, K. Paludan, and G. Laricchia,<br />
J. Phys. B: At. Mol. Opt. Phys. 34, L219<br />
(2001).<br />
[3] J. Fiol and R. E. Olson, J. Phys. B: At.<br />
Mol. Opt. Phys. 35, 1173 (2002).<br />
[4] C. Arcidiacono, A. Kövér, and G. Laricchia,<br />
Phys. Rev. Lett. 95, 223202 (2005).<br />
[5] J. Fiol and R. O. Barrachina, J. Phys. B:<br />
At. Mol. Opt. Phys. 42, 231004 (2009).<br />
[6] R. G. Pregliasco, C. R. Garibotti, and<br />
R. O. Barrachina, J. Phys. B: At. Mol.<br />
Opt. Phys. 27, 1151 (1994).<br />
29 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Estudo da ionização direta <strong>de</strong> átomos <strong>de</strong> neônio por impacto <strong>de</strong> íons <strong>de</strong> boro<br />
com energias <strong>de</strong> 1-4 MeV<br />
H. M. R. <strong>de</strong> Luna 1 , W. Wolff 1 , A.C. F. dos Santos 1 , e E. C. Montenegro 1<br />
C.C.Montanari 2,3 , e J.E.Miraglia 2,3<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, Rio <strong>de</strong> Janeiro, Brasil<br />
2 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio, Buenos Aires, Argentina<br />
3 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> Ciencias Exactas y Naturales, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Buenos Aires,<br />
Argentina<br />
hluna@if.ufrj.br<br />
Foi instalado recentemente no laboratório<br />
<strong>de</strong> colisões atômicas e moleculares do<br />
Instituto <strong>de</strong> <strong>Física</strong> da Universida<strong>de</strong> Fe<strong>de</strong>ral<br />
do Rio <strong>de</strong> Janeiro, um sistema que permite<br />
<strong>de</strong>terminar secções <strong>de</strong> choque absolutas <strong>de</strong><br />
troca <strong>de</strong> carga na colisão entre íons <strong>de</strong> carga<br />
múltipla e átomos ou moléculas. O sistema<br />
experimental compreen<strong>de</strong> <strong>de</strong> dois alvos gasosos<br />
in<strong>de</strong>pen<strong>de</strong>ntes, sendo o primeiro uma célula<br />
gasosa para medidas absolutas <strong>de</strong> secções<br />
<strong>de</strong> choque <strong>de</strong> troca <strong>de</strong> carga, e o segundo<br />
um jato gasoso efusivo acoplado a um espectrômetro<br />
<strong>de</strong> massa por tempo <strong>de</strong> vôo<br />
(TOF) para medidas em coincidência dupla<br />
do elétron ejetado – íon <strong>de</strong> recuo, íon <strong>de</strong> recuo<br />
– projétil e coincidência tripla do elétroníon<br />
<strong>de</strong> recuo-projétil (fig1).<br />
Primeiramente fizemos um estudo das<br />
secções <strong>de</strong> choque totais obtidas <strong>de</strong> forma<br />
absoluta para a troca <strong>de</strong> carga <strong>de</strong> íons <strong>de</strong> B2+<br />
colidindo com alvos <strong>de</strong> Neônio e Argônio<br />
[1]. Estes resultados serão apresentados e<br />
discutidos neste trabalho. Posteriormente esten<strong>de</strong>mos<br />
o estudo às medidas <strong>de</strong> secção <strong>de</strong><br />
choque parciais para o canal <strong>de</strong> ionização direta<br />
<strong>de</strong> alvos multieletrônicos, on<strong>de</strong> o TOF e<br />
o jato gasoso foram utilizados. Estas secções<br />
<strong>de</strong> choque foram normalizadas pelas secções<br />
<strong>de</strong> choque <strong>de</strong> captura medidas na referência<br />
[1]. Uma abordagem teórica será discutida<br />
para estes resultados preliminares.<br />
Figure 1. Linha <strong>de</strong> colisão íon-átomo, vista do sistema<br />
experimental, câmara <strong>de</strong> interação com jato gasoso,<br />
câmara <strong>de</strong> projéteis e célula gasosa<br />
Referência<br />
[1] W. Wolff, H. Luna, A.C.F.Santos and E.C.<br />
Montenegro, Phys. Rev. A 80, 032703 (2009)<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Excitación <strong>de</strong> excitones en colisiones <strong>de</strong> iones con Cristales <strong>de</strong> FLi:<br />
un mo<strong>de</strong>lo tipo-cebolla<br />
J. E. Miraglia, M.S. Gravielle<br />
Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong> Espacio (UBA y CONICET))<br />
Facultad <strong>de</strong> Ciencias Exactas y Naturales, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Buenos Aires, Argentina<br />
Ciudad Universitaria, C.C. 67, Suc. 28, 1428 Buenos Aires, Argentina<br />
email : miraglia@iafe.uba.ar<br />
Nos interesa estudiar los procesos inelásticos<br />
que ocurren cuando iones o electrones<br />
colisionan con cristales aisladores <strong>de</strong>l<br />
tipo ClNa: en particular nos concentraremos<br />
en el FLi. Un mo<strong>de</strong>lo teórico muy popular<br />
para atacar este problema consiste en consi<strong>de</strong>rar<br />
el cristal como una grilla <strong>de</strong> iones aislados<br />
<strong>de</strong> Li + y F - . Para este caso, nosotros<br />
usamos orbitales <strong>de</strong>l tipo Clementi-Roetti<br />
(ion aislado). Este mo<strong>de</strong>lo llamado grilla <strong>de</strong><br />
iones in<strong>de</strong>pendientes (GII) ha sido usado con<br />
bastante éxito. Sin embargo es incorrecto, ya<br />
que, por ejemplo, no pue<strong>de</strong> haber estados excitados<br />
correspondientes al F - , ni <strong>de</strong>scribe el<br />
potencial <strong>de</strong> Ma<strong>de</strong>lung.<br />
En este trabajo nosotros mejoramos la<br />
representación electrónica introduciendo el<br />
efecto <strong>de</strong> la grilla “vistiendo” los iones <strong>de</strong>l<br />
cristal con 44 capas colombianas correspondientes<br />
a los vecinos más próximos. En cada<br />
capa se supone una distribución <strong>de</strong> carga<br />
constante. La grilla tiene en cuenta 1330 iones<br />
teniendo cuidados en consi<strong>de</strong>rar el enjaulado<br />
(cargas fraccionales en los limites). Los<br />
iones ahora se parecen a una “cebolla” por lo<br />
que al mo<strong>de</strong>lo lo llamamos grilla <strong>de</strong> cebollas<br />
in<strong>de</strong>pendientes (GIO). Estas cebollas ahora<br />
tienen las correctas condiciones, sus estados<br />
electrónicos presentan el correcto corrimiento<br />
<strong>de</strong> Ma<strong>de</strong>lung, y cada electrón ve a gran<strong>de</strong>s<br />
distancias su propio agujero <strong>de</strong> acuerdo al<br />
mo<strong>de</strong>lo <strong>de</strong> Wannier [1]. El anión F - ahora si<br />
tiene estados excitados que en la <strong>Física</strong> <strong>de</strong>l<br />
estado sólido se los conoce como excitones.<br />
Las funciones <strong>de</strong> onda se calcularon resolviendo<br />
numéricamente la ecuación radial <strong>de</strong><br />
Schroedinger y se encontró que la solución<br />
presenta “cicatrices” correspondiente a cada<br />
capa. Se calculó el Stopping power usando la<br />
aproximación <strong>de</strong> Born (línea punteada en la<br />
figura) y la CDW-EIS (línea sólida). Los resultados<br />
se presentan en la Figura junto a los<br />
experimentos <strong>de</strong> Ba<strong>de</strong>r [2]<br />
Dos observaciones son importantes: <strong>de</strong>bido a la<br />
constante <strong>de</strong> Ma<strong>de</strong>lung, la ionización <strong>de</strong>l catión<br />
Li + es bastante importante (no lo es en el mo<strong>de</strong>lo<br />
GII), la contribución <strong>de</strong> los excitones <strong>de</strong> F - (en la<br />
figura notados con F - (2->3)@), ausente en el<br />
GII) tiene una contribución importante a energías<br />
intermedias. Se abre un tema interesante en<br />
relación al estudio <strong>de</strong> la física post-colisional<br />
<strong>de</strong> dichos excitones y su influencia en las colisiones<br />
rasantes.<br />
Referencias<br />
[1] D.L. Dexter and R. S. Knox, Excitons<br />
(Wiley, New York, 1965).<br />
[2] M. Ba<strong>de</strong>r y colaboradores, Phys. Rev. 32,<br />
103 (1953).<br />
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Fast atom diffraction from metallic surfaces<br />
M.S. Gravielle 1 , G. Bocán 2 , and R. Díez Muiño 3<br />
1 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio, CONICET, Bs. As, Argentina, and Depto <strong>de</strong> <strong>Física</strong>,<br />
FCEN, UBA.<br />
2 Centro Atómico Bariloche, CNEA and CONICET, S.C. <strong>de</strong> Bariloche, Río Negro, Argentina.<br />
3 Donostia International Physics Center (DIPC) and C. Fís. Materiales CSIC-UPV/EHU, San Sebastián,<br />
Spain.<br />
E-mail: msilvia@iafe.uba.ar<br />
1. INTRODUCTION<br />
Diffraction from crystal surfaces produced by<br />
grazing scattering of atoms in the keV energy<br />
range is nowadays attracting consi<strong>de</strong>rable attention.<br />
The first experimental evi<strong>de</strong>nces of this<br />
effect were reported for insulator surfaces [1] for<br />
which the presence of a band gap strongly suppresses<br />
inelastic electronic processes, favoring<br />
the conservation of quantum coherence. However,<br />
this diffraction effect has recently been<br />
observed at metallic materials [2,3] as well, although<br />
electron excitations were supposed to<br />
smudge interference signatures for these surfaces.<br />
The aim of this work is to study the<br />
atomic diffraction from metal surfaces by consi<strong>de</strong>ring<br />
keV nitrogen atoms impinging grazingly<br />
on Ag(111) .<br />
2. THEORETICAL MODEL<br />
To <strong>de</strong>scribe the scattering process we employ<br />
a distorted-wave mo<strong>de</strong>l - the surface-eikonal<br />
approximation [4] - that makes use of the eikonal<br />
wave function to represent the elastic collision<br />
with the surface, while the movement of the<br />
fast projectile is <strong>de</strong>scribed classically by consi<strong>de</strong>ring<br />
axially channeled trajectories for different<br />
initial conditions. The surface-eikonal T-matrix<br />
element reads:<br />
r r<br />
(eik)<br />
Tif<br />
= ∫ dRos<br />
aif<br />
( Ros<br />
),<br />
(1)<br />
where R r<br />
<strong>de</strong>termines the initial position of the<br />
os<br />
projectile on the surface plane and<br />
a<br />
if<br />
r<br />
( R<br />
os<br />
r<br />
-3<br />
) = ( 2π)<br />
∫ dt |vz<br />
( RP<br />
) |×<br />
r r r<br />
exp[ -iQ.R -i η(<br />
R )] V<br />
P<br />
P<br />
SP<br />
r<br />
( R<br />
P<br />
)<br />
(2)<br />
is the transition amplitu<strong>de</strong> associated with the<br />
r r<br />
classical path RP<br />
( Ros<br />
, t)<br />
, with Q r the projectile<br />
r<br />
momentum transfer and v z<br />
( RP<br />
) the component<br />
of the projectile velocity perpendicular to the<br />
surface plane. In Eq. (2), η ( R<br />
r P<br />
) is the eikonal-<br />
Maslov phase that takes into account the action<br />
of the projectile-surface potential V ( R<br />
r<br />
SP P)<br />
along<br />
the classical path.<br />
An accurate potential energy surface for the<br />
N/Ag(111) system was <strong>de</strong>rived from <strong>de</strong>nsity<br />
functional theory (DFT) calculations as implemented<br />
in the "Vienna Ab-initio Simulation<br />
Program" (VASP) co<strong>de</strong> [5], combined with an<br />
elaborate interpolation method [6].<br />
3. RESULTS<br />
We apply the theoretical mo<strong>de</strong>l to evaluate<br />
angular projectile distributions for impact along<br />
different low-in<strong>de</strong>x crystallographic directions.<br />
The influence of the inci<strong>de</strong>nce energy and the<br />
symmetry of the consi<strong>de</strong>red channel are both<br />
analyzed.<br />
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dP/dϕ f<br />
(arb. u.)<br />
N→Ag(111)<br />
-0,006 -0,004 -0,002 0,000 0,002 0,004 0,006<br />
Azimuthal angle ϕ f<br />
(rad)<br />
Figure 1. Azimuthal angular distribution of<br />
elastically scattered projectiles for 3 keV N atoms<br />
impinging on Ag(111) along the direction<br />
-1,-1,2, with a glancing angle ( θ i =0.4678<br />
<strong>de</strong>g.)<br />
dP/dΘ (arb. u.)<br />
N→Ag(111)<br />
E i ⊥<br />
= 0.2 eV<br />
-1.6 -1.2 -0.8 -0.4 0.0 0.4 0.8 1.2 1.6<br />
Deflection angle Θ (rad)<br />
Figure 2. Angular projectile distributions, as<br />
function of the <strong>de</strong>flection angle Θ, for N atoms<br />
scattered from Ag(111) along the direction<br />
, with E i = 0.2 eV for the inci<strong>de</strong>nce<br />
energy E i = 3.0 keV.<br />
Angular distributions of N atoms scattered<br />
from the Ag(111) surface display diffraction<br />
patterns that <strong>de</strong>pend on the axial inci<strong>de</strong>nce direction.<br />
For scattering along the channel,<br />
the angular spectrum presents interference structures,<br />
with peaks symmetrically placed with respect<br />
to the inci<strong>de</strong>nce direction. The complexity<br />
of these structures augments dramatically as E i<br />
increases up to 1.0 eV, indicating that the scattering<br />
of N atoms from a Ag surface tends to<br />
blur interference patterns more easily than for<br />
helium impact.<br />
Something similar happens when we consi<strong>de</strong>r<br />
the wi<strong>de</strong>r channel , which displays an<br />
even stronger corrugation. In addition, this inci<strong>de</strong>nce<br />
direction does not run along a symmetry<br />
axis of the surface, and this results in angular<br />
distributions displaying asymmetric structures<br />
with respect to φ f =0. Therefore, the high reactivity<br />
of N atoms favors the sensitivity of diffraction<br />
patterns to asymmetries across the<br />
channel, which in this case are originated from<br />
the contributions of target atoms from the second<br />
layer below the topmost atomic plane.<br />
We have also analyzed the contribution of<br />
inelastic processes. Our results suggest that they<br />
might not be so important as expected in the<br />
consi<strong>de</strong>red energy range, which is in accord with<br />
available experimental results. Given its high<br />
resolution in energy, diffraction of fast atoms<br />
from surfaces may therefore become a useful<br />
quality check for both insulating and metallic<br />
PESs, also providing a promising tool for surface<br />
analysis.<br />
References<br />
[1] A. Schüller et al., Phys. Rev. Lett. 98,<br />
016103 (2007); P. Rousseau et al., Phys.<br />
Rev. Lett. 98, 016104 (2007).<br />
[2] N. Bundaleski et al., Phys. Rev. Lett. 101,<br />
177601 (2008).<br />
[3] M. Busch et al., Surf. Sci. 603, L23 (2009).<br />
[4] M.S. Gravielle et al., Phys. Rev. A. 78,<br />
022901 (2008).<br />
[5] G. Kreese and J. Hafner, Phys. Rev B 47,<br />
558 (1993).<br />
[6] H.F. Busnengo et al., J. Chem. Phys. 112,<br />
7641 (2000)<br />
[2] J. B. Good, Technical Writing for Dummies<br />
(Wiley, New York, 1923).<br />
33 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Influence of light-ion irradiation on the ion track etching of polycarbonate<br />
R.S. Thomaz 1 , C. T <strong>de</strong> Souza 2 , and R. M. Papaléo 1<br />
1 Faculty of Physics, Catholic University of Rio Gran<strong>de</strong> do Sul, Porto Alegre, Brazil<br />
2 Institute of Physics, Fe<strong>de</strong>ral University of Rio Gran<strong>de</strong> do Sul, Porto Alegre, Brazil<br />
claudia.telles@ufrgs.br<br />
In this work, we report on the effect of<br />
light-ion irradiation on the pore size distribution<br />
of etched tracks produced by medium<br />
energy heavy ions in polycarbonate. Polycarbonate<br />
foils (Makrofol KG, Bayer, Germany),<br />
about 12 µm thick, were treated with 2 MeV<br />
H + ions of different fluences (1x10 13 to<br />
5x10 14 ions/cm 2 ) either before or after irradiation<br />
with a 18 MeV Au 7+ beam (at a fluence<br />
around 5x10 8 ions/cm 2 ). The heavy ion<br />
irradiation was used to produce the latent<br />
tracks in the foils and the proton beam acted<br />
as a perturbation to the <strong>de</strong>fect distribution.<br />
The sequence of irradiations was performed<br />
at a 3 MV HVEE Tan<strong>de</strong>tron accelerator at<br />
room temperature and without breaking the<br />
vacuum. The irradiated foils were etched<br />
with 6 M NaOH solution at 60 ±1 ºC for 1 to<br />
3 minutes and the etched surfaces analyzed<br />
by scanning electron microscopy. Characterization<br />
of the chemical damage and molecular<br />
weight distribution of the foils was performed<br />
by FTIR spectroscopy, gel permeation<br />
chromatography (GPC) and contact angle<br />
measurements.<br />
The microscopy results showed that the<br />
proton irradiation causes a <strong>de</strong>crease in the<br />
mean etched pore size as compared to samples<br />
bombar<strong>de</strong>d only with the Au ions<br />
(Fig.1). The reduction effect is greater at H +<br />
fluences around 2 to 5 x10 13 cm -2 , while at<br />
higher H + fluences the pore size start to grow<br />
again, as shown in Figure 2.<br />
Figure 1. SEM images of<br />
etched ion tracks on PC<br />
foils bombar<strong>de</strong>d with different<br />
2 MeV H + fluences.<br />
The samples were first<br />
bombar<strong>de</strong>d by the H + beam<br />
and subsequently irradiated<br />
with the 18 MeV Au<br />
beam to produce the etchable<br />
tracks. (a) control<br />
sample (Au beam only); (b)<br />
=5x10 12 cm -2 ; (c)=<br />
2x10 13 cm -2 ;d=5x10 13<br />
cm -2 ; (e) =2x10 14 cm -2 .<br />
34 Valparaíso, Chile
Relative diameter (a.u.)<br />
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
1.2<br />
1<br />
batch 1<br />
batch 2<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
0 5 10 13 1 10 14 1.5 10 14 2 10 14<br />
(cm -2 )<br />
Figure 2. Relative diameter of the etched pores (D()/D(0)) as a function of H + fluence , for two batches of<br />
samples.<br />
The observation of a minimum in the<br />
diameter curve is compatible with the existence<br />
of two competitive effects: one that<br />
causes the <strong>de</strong>crease in radius and is dominant<br />
at low fluences (i.e. with a large crosssection)<br />
and another that tend to increase the<br />
radial etching rate and is dominant at high<br />
fluences (with a small cross-section).<br />
The physico-chemical mechanism behind<br />
the observed effect is unclear at present.<br />
The <strong>de</strong>crease in pore size due to the proton<br />
irradiation is consistent with a reduction in<br />
the radial or bulk etch rate v B or an increase<br />
in the etching induction time. A reduced v B<br />
could be caused by e.g., crosslinking of the<br />
PC matrix induced by the proton beam. However,<br />
the GPC curves indicate the predominance<br />
of chain scission in the irradiated samples.<br />
Also negligible changes in the contact<br />
angle of the proton irradiated foils were <strong>de</strong>tected,<br />
indicating similar wetting properties.<br />
Thus the proton irradiation seems to affect<br />
the etching process in a more complex way<br />
by changing the surface properties of the PC<br />
foils.<br />
Key-words: ion track etching, polymers,<br />
polycarbonate.<br />
35 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Interacción <strong>de</strong> haces <strong>de</strong> protones con materiales <strong>de</strong> interés biológico<br />
Rafael Garcia-Molina 1 , Isabel Abril 2 , Cristian D. Denton 2 , Ioanna Kyriakou 3 , Dimitris Emfietzoglou 3<br />
1<br />
<strong>Departamento</strong> <strong>de</strong> <strong>Física</strong> – Centro <strong>de</strong> Investigación en Óptica y Nanofísica, <strong>Universidad</strong> <strong>de</strong> Murcia,<br />
E-30100 Murcia, España<br />
2<br />
Departament <strong>de</strong> <strong>Física</strong> Aplicada, Universitat d’Alacant, E-03080 Alacant, España<br />
3<br />
Medical Physics Laboratory, University of Ioannina Medical School, GR-45110 Ioannina, Grecia<br />
corresponding author: rgm@um.es<br />
La irradiación <strong>de</strong> sistemas biológicos<br />
mediante haces <strong>de</strong> partículas energéticas<br />
(electrones, positrones o iones) tiene gran interés<br />
<strong>de</strong>bido a sus numerosas aplicaciones en micro y<br />
nanodosimetría, o en física médica, como por<br />
ejemplo la radioprotección [1] y el tratamiento<br />
oncológico [2]. Así pues, es necesario estudiar y<br />
compren<strong>de</strong>r las primeras etapas físicas y<br />
químicas <strong>de</strong> la interacción <strong>de</strong> la radiación con<br />
los materiales <strong>de</strong> interés biológico para po<strong>de</strong>r<br />
pre<strong>de</strong>cir o controlar el dañado que se producirá<br />
en estos sistemas.<br />
El tratamiento radioterapéutico mediante<br />
haces <strong>de</strong> protones energéticos, u otros iones<br />
ligeros, es una alternativa que ofrece notables<br />
ventajas frente a los tratamientos usados<br />
habitualmente, los cuales emplean haces <strong>de</strong><br />
fotones o <strong>de</strong> electrones, ya que estos últimos<br />
<strong>de</strong>positan la mayor parte <strong>de</strong> su energía cerca <strong>de</strong><br />
la superficie <strong>de</strong>l tejido biológico. Sin embargo,<br />
los haces <strong>de</strong> iones <strong>de</strong> alta energía sufren poca<br />
dispersión angular y tienen una penetración bien<br />
<strong>de</strong>finida <strong>de</strong>ntro <strong>de</strong>l blanco, sufriendo un<br />
aumento significativo <strong>de</strong> la pérdida <strong>de</strong> energía al<br />
final <strong>de</strong> sus trayectorias. Así, la mayoría <strong>de</strong> la<br />
energía <strong>de</strong>l haz <strong>de</strong> iones se <strong>de</strong>posita al final <strong>de</strong><br />
su recorrido, en una pequeña región <strong>de</strong>nominada<br />
pico <strong>de</strong> Bragg, mientras que sólo una pequeña<br />
proporción <strong>de</strong> esta energía se transfiere al tejido<br />
en la región anterior y posterior a este pico.<br />
Estas características permiten controlar que la<br />
energía <strong>de</strong>l haz <strong>de</strong> iones se <strong>de</strong>posite<br />
mayoritariamente en una profundidad dada,<br />
don<strong>de</strong> se espera que actúe sobre el tumor y se<br />
reduzca el daño producido en el tejido sano.<br />
En esta comunicación se presentará el<br />
estudio <strong>de</strong> la distribución espacial <strong>de</strong> la energía<br />
<strong>de</strong>positada por un haz <strong>de</strong> protones en agua<br />
líquida. Utilizamos como blanco irradiado el<br />
agua líquida, ya que representa una parte<br />
mayoritaria en la composición <strong>de</strong> los organismos<br />
vivos, a<strong>de</strong>más <strong>de</strong> que es más simple caracterizar<br />
su respuesta a la perturbación producida por el<br />
haz <strong>de</strong> protones.<br />
Para realizar nuestro estudio utilizamos<br />
el código <strong>de</strong> simulación SEICS (Simulation of<br />
Energetic Ions and Clusters through Solids) [3-<br />
5], basado en una combinación <strong>de</strong> los métodos<br />
<strong>de</strong> Montecarlo y <strong>de</strong> Dinámica Molecular, que<br />
permite seguir dinámicamente las trayectorias<br />
<strong>de</strong>l haz <strong>de</strong> protones al incidir sobre agua líquida<br />
hasta que éstos se <strong>de</strong>tienen, <strong>de</strong>bido<br />
fundamentalmente a las interacciones con los<br />
electrones <strong>de</strong>l blanco. Así, a partir <strong>de</strong> las<br />
coor<strong>de</strong>nadas, velocida<strong>de</strong>s y carga <strong>de</strong> los<br />
proyectiles en cada instante es posible obtener la<br />
energía <strong>de</strong>positada por el proyectil en función <strong>de</strong><br />
la posición en el material irradiado.<br />
El programa SEICS incluye las<br />
principales interacciones y fenómenos que<br />
tienen lugar entre el proyectil y los átomos <strong>de</strong>l<br />
blanco: (i) fuerza <strong>de</strong> frenado electrónica<br />
(obtenida a partir <strong>de</strong>l po<strong>de</strong>r <strong>de</strong> frenado<br />
electrónico y <strong>de</strong>l straggling en la pérdida <strong>de</strong><br />
energía), (ii) colisiones elásticas con los núcleos<br />
<strong>de</strong>l blanco (que dan lugar a la <strong>de</strong>flexión <strong>de</strong>l<br />
proyectil y contribuyen a la pérdida <strong>de</strong> energía),<br />
y (iii) cambio en el estado <strong>de</strong> carga <strong>de</strong>l proyectil<br />
(<strong>de</strong>bido a los procesos <strong>de</strong> pérdida y captura<br />
electrónica entre el proyectil y el blanco).<br />
36 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
El po<strong>de</strong>r <strong>de</strong> frenado electrónico se<br />
calcula a partir <strong>de</strong>l formalismo dieléctrico y el<br />
mo<strong>de</strong>lo MELF-GOS [6] para <strong>de</strong>scribir la<br />
función <strong>de</strong> pérdida <strong>de</strong> energía <strong>de</strong>l agua líquida<br />
[7], don<strong>de</strong> se pone énfasis en la correcta<br />
<strong>de</strong>scripción <strong>de</strong>l espectro <strong>de</strong> excitaciones<br />
electrónicas a partir <strong>de</strong> los datos experimentales<br />
disponibles en la literatura [8].<br />
En la figura representamos el po<strong>de</strong>r <strong>de</strong><br />
frenado <strong>de</strong> un haz <strong>de</strong> protones en agua líquida en<br />
función <strong>de</strong> la energía inci<strong>de</strong>nte. Los símbolos<br />
correspon<strong>de</strong>n a datos experimentales <strong>de</strong> hielo.<br />
Comparamos los resultados <strong>de</strong> nuestro mo<strong>de</strong>lo<br />
MELF-GOS [5] (línea negra) con resultados<br />
semiempíricos <strong>de</strong> SRIM [9] (línea gris<br />
continua), y con datos compilados en el report<br />
<strong>de</strong> ICRU [10] (línea gris discontinua).<br />
En este trabajo hemos puesto especial<br />
énfasis en la <strong>de</strong>scripción <strong>de</strong> la energía<br />
<strong>de</strong>positada alre<strong>de</strong>dor <strong>de</strong>l pico <strong>de</strong> Bragg, por lo<br />
que nos centraremos en haces <strong>de</strong> protones con<br />
energías en la región <strong>de</strong> 0.5 MeV a 10 MeV, y<br />
analizaremos en <strong>de</strong>talle cómo las diferentes<br />
interacciones entre el haz <strong>de</strong> protones y el<br />
blanco afectan a la dosis <strong>de</strong>positada en el blanco<br />
en función <strong>de</strong> la profundidad.<br />
Por último, también analizaremos la<br />
energía <strong>de</strong>positada por el haz <strong>de</strong> protones<br />
cuando interacciona con otros materiales <strong>de</strong><br />
interés biológico, en especial el DNA.<br />
Referencias:<br />
[1] E. B. Podgorsak, Radiation Physics for<br />
Medical Physicists, Springer, Berlin, 2006.<br />
[2] M. Goitein, A. J. Lomas, E. Pedroni,<br />
Treating cancer with protons, Phys. Today 55,<br />
45 (2002).<br />
[3] S. Heredia-Avalos, R. Garcia-Molina, I.<br />
Abril, Energy-loss calculation of swift C n<br />
+<br />
(n=2–60) clusters through thin foils, Phys. Rev.<br />
A 76, 012901-1 (2007).<br />
[4] S. Heredia-Avalos, I. Abril, C. D. Denton,<br />
R. Garcia-Molina, Simulation of swift boron<br />
clusters traversing amorphous carbon foils,<br />
Phys. Rev. A 75, 012901-1 (2007).<br />
[5] R. Garcia-Molina, I. Abril, C. D. Denton, S.<br />
Heredia-Avalos, I. Kyriakou, D. Emfietzoglou,<br />
Calculated <strong>de</strong>pth-dose distributions for H + and<br />
He + beams in liquid water, Nucl. Instrum.<br />
Methods B 267, 2647 (2009).<br />
[6] I. Abril, R. Garcia-Molina, C. D. Denton, F.<br />
J. Pérez-Pérez, N. R. Arista, Dielectric<br />
<strong>de</strong>scription of wakes and stopping powers in<br />
solids, Phys. Rev. A 58, 357 (1998); S. Heredia-<br />
Avalos, R. Garcia-Molina, I. Abril, J. M.<br />
Fernán<strong>de</strong>z-Varea, Calculated energy loss of<br />
swift He, Li, B and N ions in SiO 2 , Al 2 O 3 and<br />
ZrO 2 , Phys. Rev. A 72, 052902-1(2005).<br />
[7] I. Abril, C. D. Denton, P. <strong>de</strong> Vera, I.<br />
Kyriakou, D. Emfietzoglou, R. Garcia-Molina,<br />
Effect of the Bethe surface <strong>de</strong>scription on the<br />
electronic excitations induced by energetic<br />
proton beams in liquid water and DNA, Nucl.<br />
Instrum. Methods B 268, 1763 (2010).<br />
[8] N. Watanabe, H. Hayashi, Y. Udagawa,<br />
Bethe surface of liquid water <strong>de</strong>termined by<br />
inelastic X-ray scattering spectroscopy and<br />
electron correlation effects, Bull. Chem. Soc.<br />
Jpn. 70, 719 (1997).<br />
[9] J. F. Ziegler, J. P. Biersak, M. D. Ziegler,<br />
SRIM. The Stopping and Range of Ions in<br />
Matter, SRIM Co., Chester, MD, 2008.<br />
[10] Stopping Powers and Ranges for Protons<br />
and Alpha Particles, ICRU Report 49,<br />
Bethesda, MD, 1993.<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
INTERACTION DYNAMICS OF CLUSTERS IN INTENSE<br />
LASER FIELDS<br />
D. Vernhet 1 , E. Lamour 1 , C. Prigent 1 , C. Ramond 1 , R. Reuschl 1 , J.-P. Rozet 1 ,<br />
M. Trassinelli 1 , J. Burgdörfer 2 , C. Deiss 2 , G. Schiwietz 3<br />
1 Institut <strong>de</strong>s NanoSciences <strong>de</strong> Paris, Université Pierre et Marie Curie, CNRS-UMR7588<br />
F-75252 Paris, France, EU<br />
2 Institute for Theoretical Physics, Vienna University of Technology,<br />
A-1040 Vienna, Austria, EU<br />
3 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH<br />
D-14109 Berlin, Germany, EU<br />
Large clusters, similarly to solids, couple very efficiently to intense subpicosecond laser pulses.<br />
Nearly 100 % of the laser radiation can be absorbed, leading to the observation of highly charged<br />
ions with energies reaching MeV and electrons with energies up to a few keV. A fascinating feature<br />
of this interaction is its efficiency for converting photons in the eV range to x-rays with keV<br />
energies. Whereas spectroscopy of the emitted ions maps the final stage of the Coulomb explosion,<br />
i.e. a few microseconds after the femtosecond laser pulse and the cluster disintegration, x-ray<br />
spectroscopy gives access to the dynamical evolution of the irradiated cluster on a time scale<br />
comparable to that of the laser pulse duration. Since the inner-shell vacancies are produced by<br />
electron-impact ionisation, x-ray spectroscopy can provi<strong>de</strong> insight into the electron dynamics and<br />
more precisely on the heating mechanisms, which allow electrons to gain energy as high as the innershell<br />
binding energies. KeV x-rays provi<strong>de</strong> a “thermometer” of the hot electrons in the cluster, acting<br />
as a probe of the energy distribution on the high energy si<strong>de</strong>.<br />
Rare-gas clusters- (Ar) n , (Kr) n and (Xe) n with n > 10 4 (i.e. 10-40 nm of diameter)- irradiated with<br />
intense (I
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Ionización múltiple <strong>de</strong> Ne, Ar, Kr y Xe <strong>de</strong>bido al impacto <strong>de</strong> iones H + y He +<br />
J. E. Miraglia 1,2 , C. C. Montanari 1,2 and E. C. Montenegro 3<br />
1 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio, CONICET-UBA, Buenos Aires, Argentina<br />
2 Facultad <strong>de</strong> Ciencias Exactas y Naturales, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Buenos Aires, Argentina<br />
3 Instituto <strong>de</strong> F´ısica, Universida<strong>de</strong> Fe<strong>de</strong>ral <strong>de</strong> Rio <strong>de</strong> Janeiro, Caixa Postal 68528, Rio <strong>de</strong> Janeiro, Brazil<br />
La ionización múltiple es un problema complejo<br />
<strong>de</strong>ntro <strong>de</strong> las colisiones atómicas, más aún<br />
cuando se trata <strong>de</strong> blancos pesados. Se <strong>de</strong>ben<br />
tener en cuenta muchos procesos: la ionización<br />
múltiple directa, la emisión post-colisional<br />
(post-collisional ionization o PCI) <strong>de</strong> electrones<br />
por efectos Auger o Coster–Krönig originada en<br />
la ionización <strong>de</strong> un electrón <strong>de</strong> capa interna, la<br />
emisión <strong>de</strong> electrones por shake-off, o la<br />
combinación <strong>de</strong> excitación y doble Auger. Todos<br />
estos procesos contribuyen a aumentar el estado<br />
<strong>de</strong> carga final <strong>de</strong>l blanco.<br />
Recién en los últimos años la combinación <strong>de</strong><br />
cálculos <strong>de</strong> probabilida<strong>de</strong>s <strong>de</strong> ionización con<br />
mo<strong>de</strong>los <strong>de</strong> electrón in<strong>de</strong>pendiente, y datos <strong>de</strong><br />
producción <strong>de</strong> iones multicargados en<br />
experimentos <strong>de</strong> fotoionización, ha dado una<br />
buena <strong>de</strong>scripción <strong>de</strong> los datos experimentales en<br />
la región <strong>de</strong> los MeVs [1-5]. Sin embargo los<br />
resultados teóricos abarcan los blancos Ne y Ar,<br />
mientras que los datos experimentales llegan<br />
hasta Xe.<br />
En esta oportunidad presentamos resultados<br />
teóricos <strong>de</strong> ionización simple a quintuple <strong>de</strong> Ne,<br />
Ar, Kr y Xe bombar<strong>de</strong>ados con H+ y He+ [6].<br />
Los cálculos han sido realizados empleando dos<br />
mo<strong>de</strong>los, continuum distorted wave-eikonal<br />
initial state (CDW-EIS) y primera aproximación<br />
<strong>de</strong> Born, utilizando los mismos potenciales en<br />
ambos.<br />
La contribución PCI a la ionización es<br />
introducida a través <strong>de</strong> datos experimentales <strong>de</strong><br />
<strong>de</strong>caimiento y emisión en experimentos recientes<br />
<strong>de</strong> fotoionización que utilizan técnicas <strong>de</strong><br />
coinci<strong>de</strong>ncia y tiempo <strong>de</strong> vuelo para seleccionar<br />
los procesos <strong>de</strong> ionización múltiple que siguen a<br />
la ionización simple <strong>de</strong> cierta capa <strong>de</strong> electrones<br />
<strong>de</strong>l blanco. Discutiremos también la importancia<br />
<strong>de</strong> procesos tipo shake off <strong>de</strong> los electrones <strong>de</strong> la<br />
capa <strong>de</strong> Valencia, para los cuales no hay<br />
contribución <strong>de</strong> Auger.<br />
Multiple ionization cross sections (Mb)<br />
10 3<br />
10 2<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
10 -3<br />
10 -4<br />
Kr 3+ x 10 -1 Kr 2+<br />
Kr 4+ x 10 -3<br />
Kr +<br />
10 2 10 3<br />
Energy (keV/am u)<br />
Fig 1. Multiple ionización en collision H + + Kr<br />
Los resultados obtenidos muestran que en<br />
general, la combinación <strong>de</strong> la CDW-EIS con los<br />
datos <strong>de</strong> producción <strong>de</strong> multicargados, <strong>de</strong>scriben<br />
bien la ionización múltiple para E>300 keV/<br />
amu, mostrando una clara ten<strong>de</strong>ncia a los valores<br />
<strong>de</strong> la primer aproximación <strong>de</strong> Born para altas<br />
energías.<br />
Comentaremos el llamativo resultado obtenido<br />
con la primer approximación <strong>de</strong> Born, la cual<br />
<strong>de</strong>scribe muy bien los resultados <strong>de</strong> doble y<br />
triple ionización aún en el rango <strong>de</strong> energías<br />
(50–300 keV/ amu), don<strong>de</strong> la ionización directa<br />
es la contribución dominante.<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Multiple ionization cross section (Mb)<br />
10 3 Ar 5+ x 10 -5<br />
10 2<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
10 -3<br />
10 -4<br />
10 -5<br />
10 -6<br />
Ar +<br />
Ar 2+<br />
Ar 3+ x 10 -1<br />
Ar 4+ x 10 -3<br />
Multiple ionization cross section (Mb)<br />
C avalcanti<br />
D uBois<br />
10 2 Schram for e+Ne<br />
An<strong>de</strong>rsen<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
10 -3<br />
inclu<strong>de</strong>s K-shell PCI<br />
inclu<strong>de</strong>s L-shell shake off<br />
Ne +<br />
Ne 2+<br />
Ne 3+ x 10 -1<br />
10 -7<br />
10 2 10 3<br />
Energy (keV/amu)<br />
10 2 10 3 10 4<br />
Energy (keV)<br />
Fig. 2 Ionización múltiple <strong>de</strong> Ar por He+<br />
El acuerdo con los valores experimentales es<br />
bueno, en especial para Ar y Kr para ambos<br />
iones, H+ y He+. En el caso <strong>de</strong> H+ en Xe, y He+<br />
en Ar y Kr, comparamos resultados teóricos y<br />
valores experimentales hasta ionización<br />
quíntuple.<br />
Multiple ionization cross sections (Mb)<br />
10 3 Xe +<br />
10 2<br />
Xe 2+<br />
10 1<br />
10 0<br />
Xe 3+ x 10 -1<br />
10 -1<br />
10 -2<br />
10 -3<br />
Xe 4+ x 10 -3<br />
10 -4<br />
10 -5<br />
Xe 5+ x 10 -5<br />
10 -6<br />
10 2 10 3<br />
Energy (keV/am u)<br />
Fig. 3 Ionización múltiple <strong>de</strong> Xe por H+<br />
Fig. 4 Ionización múltiple <strong>de</strong> Ne por H+<br />
El caso <strong>de</strong> Ne muestra características propias<br />
(ver figura 4). La única capa que contribuye a<br />
aumentar la ionización múltiple directa es la<br />
capa K, dado que no hay Auger <strong>de</strong> 2s y 2p. Sin<br />
embargo los resultados teóricos subestiman los<br />
valores experimentales dando muestras <strong>de</strong> que<br />
hay algún otro proceso contribuyendo a la doble<br />
y triple ionización <strong>de</strong> Ne. Mostraremos que la<br />
inclusión <strong>de</strong> shake off [7-9] darían la ten<strong>de</strong>ncia<br />
correcta para <strong>de</strong>scribir la ionización múltiple <strong>de</strong><br />
Ne a altas energías.<br />
References<br />
[1] Cavalcanti E G, et al J. Phys. B: At. Mol. Opt.<br />
Phys. 35 3937 (2002).<br />
[2] Spranger T and Kirchner T J. Phys. B: At. Mol.<br />
Opt.Phys. 37 4159 (2004).<br />
[3] Sigaud G M et al, Phys. Rev. A 69 062718<br />
(2004).<br />
[4] Galassi M E, Rivarola R D and Fainstein P D,<br />
Phys. Rev.A 75 052708 (2007).<br />
[5] Schenk G and Kirchner T, J. Phys. B: At. Mol.<br />
Opt. Phys. 42 205202 (2009)<br />
[6] Montanari C C, Montenegro E C and Miraglia J E,<br />
J. Phys. B: At. Mol. Opt. Phys. 43 165201 (2010).<br />
[7] Kochur et al, J. Phys. B: At. Mol. Opt. Phys. 35<br />
395 (2002)<br />
[8] Carlson T A and Nestor C W, Phys. Rev.A 8 2887<br />
(1973).<br />
40 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Ionization pattern in the region of the Bragg peak<br />
E C Montenegro<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, UFRJ, Caixa Postal 68528, Rio <strong>de</strong> Janeiro, 21945-970, RJ, Brazil.<br />
montenegro@if.ufrj.br<br />
Regarding direct collisional effects the<br />
penetration of heavy ions through matter is<br />
usually characterized by the energy loss,<br />
from the projectile si<strong>de</strong>, and by the number<br />
of ions produced along its trajectory, from<br />
the target si<strong>de</strong>. While energy loss measurements<br />
are numerous, embracing a large<br />
number of combinations of projectiles and<br />
targets – the latter mostly solids – ionization<br />
measurements by ions with the proper<br />
charge states, associated to the energies they<br />
have during their way through matter, are<br />
rare and restricted to gas targets, due to the<br />
nature of these measurements. For a given<br />
energy transfer by the projectile there is a<br />
large number of dynamical alternatives for a<br />
given final state of the target, making the<br />
theoretical <strong>de</strong>scription of the ionization by<br />
heavy ions more complex compared to those<br />
of energy loss. This difficulty is enhanced in<br />
the region of the Bragg peak where more<br />
than one collision channel compete on equal<br />
foot.<br />
Recently, it was shown that the shape<br />
of the Bragg peak is very much due to the<br />
energy transfer to inner target electrons [1].<br />
Although the cross section for the removal<br />
of inner electrons is small, this process involves<br />
large energy transfer. This contrasts<br />
with the ionization pattern, which is dominated<br />
by the removal of outer electrons with<br />
large cross sections and small energy transfers.<br />
In this work the differences between<br />
the patterns of energy loss and ion production<br />
are studied. Available measured cross<br />
sections for collisions of heavy ions with<br />
noble gases are used as a starting point to<br />
estimate the ionization pattern in the velocity<br />
region corresponding to the Bragg peak.<br />
This estimate requires the inclusion of other<br />
- and usually not measured - charge states<br />
which contribute to the energy <strong>de</strong>position<br />
along the particle path in this region.<br />
It is found that, in the region of the<br />
Bragg peak for energy loss, the ionization<br />
pattern is much flatter in shape as compared<br />
with that of the energy loss, as shown in<br />
Fig.1. This result points in the same direction<br />
as that observed in water [2], where essentially<br />
no peak was observed in the ion<br />
production pattern in the velocity region corresponding<br />
to the distal part of the Bragg<br />
peak. The knowledge of the shape of the<br />
ionization pattern is nee<strong>de</strong>d to interpret the<br />
effects of radiation damage by heavy ions<br />
from medical to technological applications.<br />
Figure 1. Cross section for target ions production<br />
and number of target ions produced by C ions in water.<br />
The shape is not of a single and sharp peak.<br />
References<br />
[1] E. D. Cantero, R. C. Fadanelli, C. C. Montanari,<br />
M. Behar, J. C. Eckhardt, G. H. Landschner,<br />
J. E. Miraglia and N. R. Arista, Phys.<br />
Rev. A79, 042904 (2009).<br />
[2] E. C. Montenegro, M. B. Shah, H. Luna, S.<br />
W. J. Scully, A. L. F. <strong>de</strong> Barros, J. A. Wyer, and<br />
J. Lecointre, Phys. Rev. Lett. 99, 213201 (2007).<br />
41 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Laboratorio Tan<strong>de</strong>m <strong>de</strong> 1.7MV <strong>de</strong>l Centro Atómico Bariloche<br />
G. Bernardi, D. Fregenal, P. Focke y S. Suárez 1<br />
Comisión Nacional <strong>de</strong> Energía Atómica(CNEA) –Centro Atómico Bariloche(CAB)<br />
Consejo nacional <strong>de</strong> Investigaciones Científicas y <strong>Técnica</strong>s (CONICET)<br />
Av. E. Bustillo 9500, S.C. <strong>de</strong> Bariloche, Río Negro – Argentina.<br />
1 <strong>Universidad</strong> nacional <strong>de</strong> Cuyo – Instituto Balseiro<br />
email address corresponding author: suarez@cab.cnea.gov.ar<br />
El laboratorio <strong>de</strong> Colisiones Atómicas<br />
<strong>de</strong>l Centro Atómico Bariloche (CAB) ha incorporado<br />
recientemente un acelerador Tan<strong>de</strong>m<br />
<strong>de</strong> 1.7MV, una línea <strong>de</strong> microhaz con<br />
una cámara para análisis y caracterización <strong>de</strong><br />
materiales y otros equipamientos adicionales<br />
para estudios <strong>de</strong> colisiones atómicas y superficies,<br />
entre los cuales se <strong>de</strong>stacan una cámara<br />
<strong>de</strong> UHV con espectrómetro <strong>de</strong> análisis Auger,<br />
con manipulador e intercambiador <strong>de</strong><br />
muestras y una línea <strong>de</strong> espectroscopía <strong>de</strong><br />
electrones e iones ya utilizada en una gran<br />
cantidad <strong>de</strong> investigaciones [1].<br />
En esta presentación se mostrarán las<br />
nuevas facilida<strong>de</strong>s experimentales, técnicas<br />
implementadas (PIXE, RBS, ERDA, NRA,<br />
Channeling, etc) y sus potencialida<strong>de</strong>s, dando<br />
ejemplos <strong>de</strong> algunas <strong>de</strong> las aplicaciones ya<br />
realizadas en campos <strong>de</strong> la biología, arqueología,<br />
física forense, tecnología <strong>de</strong> celdas solares,<br />
<strong>de</strong>terminación <strong>de</strong> espesores <strong>de</strong> óxidos y<br />
po<strong>de</strong>res <strong>de</strong> frenamiento, etc.<br />
El uso combinado <strong>de</strong> RBS y PIXE, por<br />
ejemplo, ha permitido estudiar la composición<br />
<strong>de</strong> sedimentos marinos <strong>de</strong> la costa patagónica,<br />
con el propósito <strong>de</strong> investigar posibles<br />
fuentes <strong>de</strong> contaminación humana. Estos<br />
resultados han sido comparados con estándares<br />
provistos por la IAEA [2].<br />
La composición multicapas <strong>de</strong> una celda<br />
solar, así como sus características, fueron<br />
medidas y los resultados corroborados con un<br />
estudio <strong>de</strong> perfiles <strong>de</strong> profundidad (<strong>de</strong>pth<br />
profiling) realizado por ciclos <strong>de</strong> sputtering<br />
<strong>de</strong> Ar a 3.5keV y analisis por fotoemisión<br />
XPS. La consistencia entre ambos estudios es<br />
notable, resaltándose los resultados obtenidos<br />
con la técnica RBS por su simplicidad, pocas<br />
horas <strong>de</strong> adquisición y análisis y por tratarse<br />
<strong>de</strong> un estudio no <strong>de</strong>structivo<br />
Figure 1. Vista parcial <strong>de</strong>l acelerador Tan<strong>de</strong>m y la<br />
línea <strong>de</strong>l microhaz con la cámara multipropósito<br />
RC43 <strong>de</strong> la empresa NEC para caracterización <strong>de</strong><br />
materiales.<br />
Las técnicas PIXE y RBS han sido<br />
también utilizadas para el análisis <strong>de</strong> cuentas<br />
<strong>de</strong> collares <strong>de</strong> la cultura Tehuelche con el<br />
propósito <strong>de</strong> diferenciar el origen marítimo o<br />
lacustre <strong>de</strong> las valvas utilizadas como material<br />
<strong>de</strong> construcción <strong>de</strong> las mismas. Se realizaron,<br />
a<strong>de</strong>más, estudios <strong>de</strong> residuos <strong>de</strong> disparos<br />
los cuales aportaron resultados a una causa<br />
policial. También fueron efectuados varios<br />
análisis <strong>de</strong> diferentes carburos <strong>de</strong> base Fe y<br />
W, óxidos <strong>de</strong> Zr y vidrios varios para estandarización<br />
<strong>de</strong> futuros análisis forenses [3].<br />
Algunos <strong>de</strong> estos resultados serán presentados<br />
como ejemplos.<br />
En el campo <strong>de</strong> las colisiones atómicas,<br />
entretanto, se han realizado mediciones <strong>de</strong><br />
emisión <strong>de</strong> electrones binarios por colisión <strong>de</strong><br />
42 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
H+, Li q+ (q= 1, 2 y 3) y Al q+ (q0= 1, 2 y 3)<br />
con blancos <strong>de</strong> He con el propósito <strong>de</strong> observar<br />
posibles interferencias coherentes <strong>de</strong> contribuciones<br />
<strong>de</strong> corto y largo rango <strong>de</strong>l potencial<br />
perturbativo <strong>de</strong>l proyectil [4]. Si bien un<br />
efecto tal ha sido observado experimentalmente<br />
para proyectiles multicargados, aunque<br />
parcialmente vestidos, como el U 21+ con<br />
energías <strong>de</strong> 1MeV/u [5], el objetivo <strong>de</strong> este<br />
estudio es investigar la posibilidad <strong>de</strong> tales<br />
interferencias con proyectiles con cargas pequeñas<br />
y energías menores. Se mostrarán, a<br />
modo <strong>de</strong> referencia, los resultados obtenidos<br />
con proyectiles <strong>de</strong>snudos (H + y Li 3+ ) y su<br />
comparación con cargas menores (Li 2+ , Li + )<br />
para la energía 440 keV/u. Se presentarán<br />
también resultados obtenidos con proyectiles<br />
más pesados Al q+ para 100 y 200 keV/u. Para<br />
cada uno <strong>de</strong> los sistemas mencionados se realizaron<br />
mediciones <strong>de</strong> distribuciones doblemente<br />
diferenciales, en ángulo y energía, <strong>de</strong><br />
los electrones emitidos cubriendo prácticamente<br />
el rango angular completo y para<br />
energías extendidas más allá <strong>de</strong>l pico <strong>de</strong> colisión<br />
binaria.<br />
Dentro <strong>de</strong>l conocido proceso <strong>de</strong> transferencia<br />
<strong>de</strong> electrones al continuo <strong>de</strong>l proyectil,<br />
se ha investigado la emisión al continuo<br />
<strong>de</strong> estados Rydberg altamente excitados en<br />
proyectiles <strong>de</strong> Si q+ sobre blancos <strong>de</strong> He y Ar.<br />
Estos resultados se han comparado con los<br />
obtenidos con otros proyectiles (H + , Li q+ ,<br />
Al q+ , C q+ ). Mientras que los proyectiles H + ,<br />
Li q+ y Al q+ , muestran la típica forma <strong>de</strong> cúspi<strong>de</strong><br />
para el proceso <strong>de</strong> captura <strong>de</strong> electrones<br />
al continuo, el Si q+ y el C q+ presentan picos<br />
satélites <strong>de</strong> muy baja energía relativa al proyectil,<br />
<strong>de</strong>formando significativamente el pico<br />
<strong>de</strong> captura al continuo. La Figura 2 muestra<br />
el resultado obtenido para 700 keV Si + sobre<br />
He.<br />
Se observa que, al aumentar la energía<br />
<strong>de</strong>l proyectil, el pico central, correspondiente<br />
a la velocidad <strong>de</strong>l proyectil, crece en magnitud<br />
y domina el espectro <strong>de</strong> emisión, aunque<br />
mantiene una forma simétrica, no divergente,<br />
y con picos satélites que no pue<strong>de</strong>n i<strong>de</strong>ntificarse<br />
con la resolución <strong>de</strong>l espectrómetro utilizado[1].<br />
Resultados <strong>de</strong> auto-emisión <strong>de</strong><br />
electrones en estados excitados han sido reportados<br />
por Kawatsura y colaboradores [6]<br />
para Si, S, Sc altamente ionizados con blancos<br />
<strong>de</strong> He y láminas <strong>de</strong> C, sin embargo las<br />
líneas o picos <strong>de</strong> emisión (Coster-Kronig) en<br />
el sistema <strong>de</strong>l proyectil, por ellos reportadas,<br />
correspon<strong>de</strong>n a energías que superan los tres<br />
ór<strong>de</strong>nes <strong>de</strong> magnitud a las observadas en<br />
nuestros experimentos.<br />
Figure 2. Emisón <strong>de</strong> electrons con la velocidad <strong>de</strong>l<br />
proyectil para la colisión 700keV Si + +He.<br />
Finalmente, se comentarán algunas<br />
perspectivas <strong>de</strong>l crecimiento <strong>de</strong>l laboratorio y<br />
otros resultados obtenidos con un acelerador<br />
<strong>de</strong> menores energías.<br />
Referencias<br />
[1] G. Bernardi et al, Rev. Sci. Instrum. 67,<br />
1761(1996).<br />
[2] A Mannan et al, IAEA Report Nº IAEA-<br />
356, 223 (2007).<br />
[3] M.J. Bailey and C. Jeynes, Nucl. Instrum.<br />
and Methods B, 267, 2265 (2009).<br />
[4] J M Monti, R D Rivarola and P D Fainstein,<br />
J. Phys. B: At. Mol. Opt. Phys. 41<br />
(2008) 201001<br />
[5] C O Reinhold et al, Phys. Rev Lett. 66,<br />
1842(1991).<br />
[6] M Sataka et al, J. Phys. B: At. Mol. Opt.<br />
Phys. 35, 267(2002) y referencias citadas.<br />
43 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
LPA stopping power of swift ions in solids. Mo<strong>de</strong>ling the inhomogeneous<br />
electron gas<br />
J. M. Fernán<strong>de</strong>z-Varea 1 , C. D. Denton 2 , I. Abril 2 and R. Garcia-Molina 3<br />
1<br />
Facultat <strong>de</strong> <strong>Física</strong> (ECM and ICC), Universitat <strong>de</strong> Barcelona, Diagonal 647, E-08028 Barcelona, Spain<br />
2<br />
Departament <strong>de</strong> <strong>Física</strong> Aplicada, Universitat d’Alacant, Apartat 99, E-03080 Alacant, Spain<br />
3<br />
<strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>-CIOyN, <strong>Universidad</strong> <strong>de</strong> Murcia, Apartado 4021, E-30080 Murcia, Spain<br />
email address corresponding author: jose@ecm.ub.es<br />
The stopping of swift ions in solids is<br />
still a subject of intense research in spite of<br />
the many <strong>de</strong>ca<strong>de</strong>s elapsed since the pioneering<br />
works of Bohr, Bethe and others. There<br />
are numerous theories that <strong>de</strong>scribe the energy<br />
loss of a heavy charged particle (charge<br />
Z 1 , velocity v) in a free-electron gas (FEG) of<br />
uniform <strong>de</strong>nsity ρ, such as the dielectric<br />
formalism or non-linear methods [1,2]. If the<br />
projectile penetrates a medium with a varying<br />
local electron <strong>de</strong>nsity, e.g. a crystalline solid,<br />
the local-plasma approximation (LPA) lets us<br />
express the stopping power as<br />
where V is the volume of the unit cell.<br />
We find it convenient to split ρ(r) into<br />
contributions from atomic inner shells (cores)<br />
and weakly-bound (valence) electrons, i.e.<br />
difficult to implement. As an alternative, the ab<br />
initio TB-LMTO method [4,5] has been used occasionally<br />
to mo<strong>de</strong>l the stopping of swift ions in<br />
channeling conditions [6].<br />
In the present work, Roothaan-Hartree-<br />
Fock wave function [7] are employed to mo<strong>de</strong>l<br />
the electron <strong>de</strong>nsity of the cores. In turn, the<br />
program TB-LMTO-ASA [4,5] is adopted to<br />
generate the 3D valence-electron <strong>de</strong>nsities.<br />
These methods are used to calculate the electron<br />
<strong>de</strong>nsities of solid Al, Si, Cu, Ag, and Au.<br />
In or<strong>de</strong>r to avoid computing the LPA<br />
stopping power due to valence electrons as a 3D<br />
integral, the probability distribution function<br />
p(ρ v ) is first extracted from ρ v (r) because then<br />
Figure 1 shows the p(ρ v ) distributions of solid<br />
Al, Si, and Cu.<br />
Neglecting the overlap between the two electron<br />
<strong>de</strong>nsities, the LPA stopping power may<br />
be written as<br />
Electrons in the cores are barely disturbed by the<br />
solid-state environment. Hence, the corresponding<br />
<strong>de</strong>nsity is spherically symmetrical and can<br />
be evaluated straightforwardly using atomic<br />
wave functions. On the other hand, the spatial<br />
distribution of valence electrons is strongly affected<br />
by aggregation effects. and may display a<br />
non-negligible anisotropy. The 3D electron<br />
<strong>de</strong>nsity can be calculated with the Dawson-<br />
Stewart-Coppens formalism. However, so far<br />
this method has found only limited application<br />
(see e.g. reference [3]), possibly because it is<br />
Figure 1. Probability distribution function<br />
p(ρ v ) of solid Al, Si, and Cu, extracted from the<br />
3D valence-electron <strong>de</strong>nsities calculated with the<br />
TB-LMTO-ASA program.<br />
44 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
As an application of the presented<br />
methods we investigate the stopping power of<br />
H and He ions in the aforementioned solids.<br />
For the sake of simplicity we resort to the<br />
well-known relation [1,2,8,9])<br />
which is the low-velocity form of non-linear<br />
theory. The transport cross section is evaluated<br />
numerically from phase shifts <strong>de</strong>termined<br />
in a self-consistent way so as to satisfy<br />
the Frie<strong>de</strong>l sum rule [1,2,8,9].<br />
The LPA friction coefficient Q=S/v is<br />
found to change 4% in the case of slow H and<br />
He ions in Al compared to the values obtained<br />
assuming a constant <strong>de</strong>nsity for the<br />
valence electrons. In turn, for H and He in Si<br />
the change amounts to 12% and 16%, respectively.<br />
These trends are to be expected in<br />
sight of the valence electron <strong>de</strong>nsity distributions<br />
displayed in figure 1.<br />
Work is in progress to explore further<br />
consequences of the presented <strong>de</strong>composition<br />
of the local electron <strong>de</strong>nsity. In particular, the<br />
stopping power at higher velocities is being<br />
studied with the non-linear mo<strong>de</strong>l of Nagy<br />
and Apagyi [10].<br />
[8] P. M. Echenique, R. M. Nieminen, J. C.<br />
Ashley, and R. H. Ritchie, Phys. Rev. A 33, 897<br />
(1986).<br />
[9] J. Calera-Rubio, A. Gras-Martí, and N. R.<br />
Arista, Nucl. Instrum. Meth. B 93, 137 (1994).<br />
[10] I. Nagy and B. Apagyi, Phys. Rev. A 58,<br />
R1653 (1998).<br />
References<br />
[1] P. M. Echenique, F. Flores, and R. H. Ritchie,<br />
Solid State Phys. 43, 229 (1990).<br />
[2] Adv. Quantum Chem., volumes 45 and 46<br />
(2004).<br />
[3] J. Sillanpää, J. Peltola, K. Nordlund, J.<br />
Keinonen, and M. J. Puska, Phys. Rev. B 63,<br />
134113 (2001).<br />
[4] O. K. An<strong>de</strong>rsen and O. Jepsen, Phys. Rev.<br />
Lett. 53, 2571 (1984).<br />
[5] http://www.fkf.mpg.<strong>de</strong>/an<strong>de</strong>rsen/<br />
[6] J. E. Valdés, P. Vargas, C. Celedón, E.<br />
Sánchez, L. Guillemot, and V. A. Esaulov, Phys.<br />
Rev. A 78, 032902 (2008).<br />
[7] C. F. Bunge, J. A. Barrientos, and A. V.<br />
Bunge, At. Data Nucl. Data Tables 53, 113<br />
(1993).<br />
45 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Manipulation of magnetic and electronic properties of Ga 1 - x Mn x As by ionbeam<br />
irradiation<br />
M. M. Sant’Anna 1 , T. G. Rappoport 1 , E. H. C. P. Sinnecker 1 , M. P. Pires 1 , G. M. Penello<br />
1 , D. E. R. Souza 1 , S. L. A. Mello 1 , J. B. S. Men<strong>de</strong>s 1 , J. K. Furdyna 2 , and X. Liu 2<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, Rio <strong>de</strong> Janeiro 21941-909, RJ, Brazil<br />
2 Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA<br />
email address corresponding author: mms@if.ufrj.br<br />
Spintronics relies on the simultaneous<br />
use of both charge and spin <strong>de</strong>grees of freedom<br />
of charge carriers. New materials have<br />
been <strong>de</strong>veloped in recent years in or<strong>de</strong>r to<br />
create a path towards the realization of spintronic<br />
<strong>de</strong>vices. The Ga 1-x Mn x As is one among<br />
those materials. It has a crystalline structure<br />
similar to Gallium Arseni<strong>de</strong> with a small<br />
fraction of the Ga atoms replaced by Mn atoms.<br />
The sites with Mn are diluted in the<br />
original Ga 1-x Mn x As lattice.<br />
The Ga 1-x Mn x As is a semiconductor<br />
that also has magnetic characteristics. Its ferromagnetism,<br />
however, is not a consequence<br />
of direct Mn-Mn interactions. The relevant<br />
Mn-Mn interaction is mediated by the holes<br />
that are introduced by the Mn substitutional<br />
to Ga (Mn Ga ). Thus, Mn Ga atoms in Ga 1-<br />
xMn x As provi<strong>de</strong>, at the same time, the holes<br />
and the magnetic moments that are crucial for<br />
the existence of magnetism in the material.<br />
Intersticial Mn atoms, and other kinds of <strong>de</strong>fects,<br />
on the other hand, <strong>de</strong>crease the <strong>de</strong>nsity<br />
of carriers in the material. As a consequence,<br />
magnetism is also <strong>de</strong>creased when Mn atoms<br />
are displaced from Ga substitutional positions.<br />
In practice, perfect crystalline Ga 1-<br />
xMn x As is never grown and un<strong>de</strong>rstanding the<br />
role of <strong>de</strong>fects in their magnetic and chargetransport<br />
properties is fundamental in or<strong>de</strong>r<br />
to control the behavior of this material (e.g.<br />
[1]). Ion beams can displace the Mn atoms in<br />
a controllable way. Thus, we have studied<br />
Ga 1-x Mn x As with the controlled introduction<br />
of <strong>de</strong>fects by irradiating the samples with energetic<br />
ion beam. Our recent study (Ref. [2])<br />
focuses on the low-carrier-<strong>de</strong>nsity regime,<br />
starting with as-grown Ga 1-x Mn x As films and<br />
<strong>de</strong>creasing even further the number of carriers,<br />
through a sequence of irradiation doses.<br />
We performed in situ room-temperature resistivity<br />
measurements as a function of the ion<br />
dose (Fig. 1).We have also studied the magnetization<br />
as a function of temperature and of<br />
the irradiation ion dose. We observe that both<br />
magnetic and transport properties of the samples<br />
can be experimentally manipulated by<br />
controlling the ion-beam parameters.<br />
Rs (Ω/sq)<br />
10 5 x nom<br />
=5%<br />
Ga 1-x Mn x As<br />
10 4<br />
10 3<br />
Li + (700 keV) + Ga 1-x<br />
Mn x<br />
As<br />
Li + beam<br />
p inicial<br />
=2×10 14 cm -2<br />
l = 4 mm<br />
d = 100 nm<br />
10 10 10 11 10 12 10 13 10 14 10 15<br />
Dose (Li + /cm 2 )<br />
Figure 1. Sheet Resistance as a function of the irradiation<br />
dose measured in-situ for 700 keV Li + projectiles.<br />
The sample is a 100 nm Ga 1-x Mn x As thin film<br />
grown by MBE on a GaAs substrate.<br />
References<br />
[1] K. Sato et al., Rev. Mod Phys. 82, 1633<br />
(2010).<br />
[2] E. H. C. P. Sinnecker et al., Phys.<br />
Rev. B. 81, 245203 (2010).<br />
46 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Medidas da distribuição <strong>de</strong> energia <strong>de</strong> moléculas e fragmentos moleculares<br />
por espectroscopia <strong>de</strong> tempo <strong>de</strong> vôo com extração retardada.<br />
Natalia Ferreira (1) , L. Sigaud (1) , V. L. B. <strong>de</strong> Jesus (2) , W. Wolff (1) , M. B. Shah (3) ,<br />
and E. C. Montenegro (1)<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, P.O. 68528, 21941-972 Rio <strong>de</strong> Janeiro, RJ, Brasil<br />
2 Instituto Fe<strong>de</strong>ral <strong>de</strong> Educação, Ciência e Tecnologia, R. Lucio Tavares 1045, 26530-060 Nilópolis, RJ, Brasil<br />
3 The Queen’s University Belfast, University Road Belfast, BT7 1NN, Northern Ireland, UK<br />
email para correspondência: natalia@if.ufrj.br<br />
Este trabalho apresenta medidas diretas da<br />
distribuição <strong>de</strong> energia <strong>de</strong> moléculas e fragmentos<br />
moleculares utilizando uma técnica <strong>de</strong> espectroscopia<br />
por tempo <strong>de</strong> vôo com extração retardada,<br />
que permite um estudo <strong>de</strong>talhado da dinâmica<br />
<strong>de</strong> colisões com moléculas.<br />
A metodologia proposta tem maior<br />
sensibilida<strong>de</strong> para fragmentos <strong>de</strong> baixa energia<br />
<strong>de</strong>s<strong>de</strong> térmicos, supra térmicos, até alguns eV,<br />
diferente <strong>de</strong> métodos tradicionais que são mais<br />
sensíveis a fragmentos com energias mais altas.<br />
A montagem experimental utilizada é<br />
baseada em um espectrômetro <strong>de</strong> massa por<br />
tempo <strong>de</strong> vôo, on<strong>de</strong> a interação ocorre <strong>de</strong>ntro <strong>de</strong><br />
uma célula com o gás <strong>de</strong> interesse em equilíbrio<br />
térmico com o ambiente. O pulso <strong>de</strong> elétrons é<br />
intercalado com um pulso <strong>de</strong> extração, que po<strong>de</strong><br />
ser dado imediatamente após a passagem do feixe<br />
<strong>de</strong> elétrons ou com um atraso temporal variável.<br />
A função distribuição <strong>de</strong> velocida<strong>de</strong>s é obtida<br />
através dos produtos medidos em função do<br />
tempo <strong>de</strong> retardo pela mo<strong>de</strong>lagem da difusão dos<br />
íons a partir da zona <strong>de</strong> interação.<br />
Resultados preliminares, utilizando a<br />
molécula N 2 , mostram que a metodologia<br />
reproduz com fi<strong>de</strong>lida<strong>de</strong> a distribuição <strong>de</strong><br />
energia térmica (<strong>de</strong> Maxwell -Boltzmann) para a<br />
molécula mãe simplesmente ionizada N + 2 . Como<br />
po<strong>de</strong> ser visto na figura, os círculos fechados são<br />
o resultado teórico para distribuição <strong>de</strong><br />
velocida<strong>de</strong>s <strong>de</strong> MB, e os círculos abertos são os<br />
dados experimentais.<br />
O pico <strong>de</strong> razão massa/ carga = 14<br />
possui contribuições do fragmento N + e da<br />
molécula mãe duplamente ionizada, N ++ 2 , que<br />
não são distinguíveis usando a espectroscopia <strong>de</strong><br />
massa usual. Através da análise da função<br />
distribuição <strong>de</strong> velocida<strong>de</strong> é possível i<strong>de</strong>ntificar<br />
a contribuição <strong>de</strong> cada um <strong>de</strong>sses íons. Na figura<br />
as distribuições <strong>de</strong> velocida<strong>de</strong>s do fragmento N +<br />
e da molécula N ++ 2 se somam e são comparadas<br />
aos dados experimentais, como indicado.<br />
A questão da estabilida<strong>de</strong> <strong>de</strong> moléculas<br />
++,<br />
pequenas, como o N 2 duplamente carregadas<br />
vem sendo estudada utilizando-se diferentes<br />
técnicas: com moléculas contendo isótopos [1],<br />
através da análise <strong>de</strong> sua meia vida em<br />
aceleradores [2], e, mais recentemente,<br />
utilizando <strong>de</strong>tectores especiais supercondutores<br />
[3]. O método aqui proposto é uma alternativa<br />
++,<br />
simples para tratar o problema. Como o N 2<br />
possui velocida<strong>de</strong> térmica, po<strong>de</strong>mos facilmente<br />
i<strong>de</strong>ntificá-lo, pois é nesta faixa que a<br />
metodologia <strong>de</strong>senvolvida é mais precisa.<br />
Referencias:<br />
Figura: Frações <strong>de</strong> íons coletados em função do tempo <strong>de</strong><br />
retardo. A molécula mãe, N 2<br />
q+<br />
tem distribuição <strong>de</strong> energia<br />
<strong>de</strong> Maxwell-Boltzmann (MB). O fragmento N + tem uma<br />
função distribuição <strong>de</strong> velocida<strong>de</strong>s <strong>de</strong>pen<strong>de</strong>nte do canal <strong>de</strong><br />
fragmentação.<br />
[1] T.D. Märk, J. Chem. Phys., vol 23, n. 9 (1975)<br />
[2] D Mathur et al., J. Phys. B At. Mol, Opt. Phys. 28<br />
3415-3426. (1995)<br />
[3] Shiki et al, J. Mass Spectrom., 43: 1686–1691<br />
(2008)<br />
47 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Perda <strong>de</strong> energia <strong>de</strong> elétrons em água<br />
André C. Tavares 1 , E. C. Montenegro 2<br />
1 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Pontifícia Universida<strong>de</strong> Católica do Rio <strong>de</strong> Janeiro, CP. 38071, Rio <strong>de</strong><br />
Janeiro, RJ, 22452-970, Brasil<br />
2 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, CP. 6852, Rio <strong>de</strong> Janeiro, RJ, 21945-970,<br />
Brasil<br />
email address corresponding author: andre.tavares@vdg.fis.puc-rio.br<br />
O conhecimento da perda <strong>de</strong><br />
energia <strong>de</strong> elétrons em água é fundamental<br />
para <strong>de</strong>terminar os efeitos indiretos <strong>de</strong><br />
praticamente todos os tipos <strong>de</strong> radiações<br />
ionizantes em tecidos biológicos.<br />
Apesar disso, não existem medidas<br />
diretas <strong>de</strong> perda <strong>de</strong> energia em água para<br />
energias <strong>de</strong> impacto nas cercanias do pico<br />
<strong>de</strong> Bragg, principalmente porque o alcance<br />
<strong>de</strong>sses elétrons em água liquida é muito<br />
pequeno, abaixo <strong>de</strong> 50 nm para energias<br />
menores que 1 keV, conforme mostrado na<br />
fig. 1 [1].<br />
associadas à formação dos fragmentos<br />
H 2 O + , OH + , O + e H + . Para cada fragmento<br />
produzido, existem orbitais específicos<br />
responsáveis pela quebra molecular. Po<strong>de</strong>se<br />
então relacionar a quantida<strong>de</strong> <strong>de</strong> energia<br />
<strong>de</strong>positada por elétron inci<strong>de</strong>nte, em um<br />
<strong>de</strong>terminado orbital, com a quantida<strong>de</strong> <strong>de</strong><br />
fragmentos produzidos pela ionização <strong>de</strong>ste<br />
orbital.<br />
Figura 1. Variação do alcance <strong>de</strong> penetração<br />
do elétron em água líquida como função da<br />
energia inicial do elétron entre 0,2 eV a 150<br />
keV. [1]<br />
A maioria dos valores disponíveis<br />
na literatura para a perda <strong>de</strong> energia nessa<br />
região é obtida através <strong>de</strong> cálculos [ver, por<br />
exemplo, 2 e 3] e somente nos últimos<br />
anos foram <strong>de</strong>spendidos esforços para a<br />
obtenção <strong>de</strong> medidas <strong>de</strong> transferência <strong>de</strong><br />
energia em vapor <strong>de</strong> água [4]. Neste<br />
trabalho, apresentamos uma nova<br />
abordagem para obter a transferência <strong>de</strong><br />
energia <strong>de</strong> elétrons com energias na região<br />
do pico <strong>de</strong> Bragg, para os diversos orbitais<br />
moleculares da água, utilizando os<br />
resultados <strong>de</strong> medidas da produção <strong>de</strong><br />
fragmentos originários da ionização da<br />
molécula. A partir dos valores obtidos <strong>de</strong><br />
perda <strong>de</strong> energia por orbital, é calculada a<br />
perda <strong>de</strong> energia total além das parciais<br />
Figura 2. Comparação entre os resultados <strong>de</strong><br />
perda <strong>de</strong> energia obtidos através do método<br />
proposto, consi<strong>de</strong>rando vários conjuntos <strong>de</strong><br />
dados experimentais para a fragmentação, e<br />
resultados teóricos.<br />
Nosso método permite, pela<br />
primeira vez, uma avaliação abrangente <strong>de</strong><br />
todos os dados experimentais disponíveis<br />
na literatura sobre a fragmentação da<br />
molécula <strong>de</strong> H 2 O, mostrando que existem<br />
gran<strong>de</strong>s discrepâncias entre a transferência<br />
<strong>de</strong> energia obtida através das medidas com<br />
vapor <strong>de</strong> água e os diversos cálculos <strong>de</strong><br />
perda <strong>de</strong> energia, principalmente para<br />
energias <strong>de</strong> impacto na região e abaixo do<br />
pico <strong>de</strong> Bragg, fig. 2.<br />
Referencias<br />
[1] Meesungnoen, J. and Mankhetkon, S.,<br />
Radiation Research 158 (2002) 657.<br />
[2] La Verne, J.A. and Mozum<strong>de</strong>r, A.,<br />
Radiation Research 96 (1983) 219.<br />
[3] NIST database http://physics.nist.gov/cgi<br />
bin/Star/e_table.pl<br />
[4] Muñoz, A. et al., Phys. Rev. A 76<br />
(2007) 052707.<br />
48 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Plasmon excitation in single walled carbon nanotubes by charged particles<br />
S. Segui 1 , D. J. Mowbray 2 , 3 , J. L. Gervasoni 1 , Z. L. Mišković 2 and N. R. Arista 1<br />
1<br />
Centro Atómico Bariloche (CNEA) 8400 S.C. <strong>de</strong> Bariloche, Río Negro, Argentina<br />
2<br />
Department of Applied Mathematics, Univ. of Waterloo, Waterloo, Ontario, Canada<br />
3<br />
Nano-Bio Spectroscopy Group, Depto. <strong>Física</strong> <strong>de</strong> Materiales, Univ. País Vasco, San Sebastián, Spain<br />
email address corresponding author: segui@cab.cnea.gov.ar<br />
The excitation of plasmons in singleand<br />
multi-walled nanotubes has been the<br />
object of several experimental and theoretical<br />
studies in recent years, since it plays an<br />
important role in a variety of interesting<br />
phenomena, such as probing the nanotube<br />
response by EELS, formation of electron<br />
image states, etc.<br />
Due to the geometry of single-walled<br />
nanotubes, and the characteristics of the<br />
electronic structure of carbonaceous<br />
nanostructures (with σ and π orbitals), the<br />
excitation of plasmons is conveniently<br />
<strong>de</strong>scribed by a two-fluids formulation of the<br />
hydrodynamic mo<strong>de</strong>l. In this formulation, σ<br />
and π electrons are treated as separate twodimensional<br />
fluids constrained to the same<br />
cylindrical surface. The electrostatic<br />
interaction between the fluids gives rise to<br />
splitting of the plasmon frequencies into two<br />
groups of distinct energies.<br />
In this work we present a quantization<br />
of the two-fluids hydrodynamic mo<strong>de</strong>l [1].<br />
This procedure allows us to obtain the<br />
average number of plasmons excited by a fast<br />
charged particle impinging on the nanotube at<br />
different positions. We also calculate several<br />
other quantities, such as the stopping power,<br />
energy loss spectra and total energy loss,<br />
which could be compared with experimental<br />
measurements. We study the effect of various<br />
parameters, such as the velocity of the<br />
inci<strong>de</strong>nt particle, the impact parameter, the<br />
inclination of the trajectory with respect to<br />
the tube’s axis, etc. Figure 1 shows the total<br />
energy loss suffered by a proton passing near<br />
a 7 Å radius nanotube, as a function of the<br />
inci<strong>de</strong>nt velocity v, for (a) perpendicular and<br />
(b) oblique trajectory, and different minimum<br />
distances from the tube's axis.<br />
Figure 1. Total energy loss E l o s s versus<br />
speed v for proton trajectory passing near<br />
a SWCNT of radius R=7 Å with an angle<br />
relative to the tube's axis of (a) 90° and<br />
(b) 45°, at the minimum separation of r m i n<br />
= 7.5 Å (top), 8.0, 8.5, 9.0, 9.5, 10.0, and<br />
10.5 Å (bottom).<br />
References<br />
[1] D. J. Mowbray, S. Segui, J. L. Gervasoni, Z.<br />
L. Mišković and N. R. Arista, Phys. Rev. B. 82,<br />
035405 (2010).<br />
49 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Processos <strong>de</strong> Troca <strong>de</strong> Carga na Ionização Múltipla <strong>de</strong> Gases Nobres por<br />
Íons <strong>de</strong> C 3 +<br />
G. M. Sigaud 1 , A. C. F. Santos 2 , M. M. Sant’Anna 2 , W. S. Melo 3 , E. C. Montenegro 2<br />
1 <strong>Departamento</strong>. <strong>de</strong> <strong>Física</strong>, Pontifícia Universida<strong>de</strong> Católica do Rio <strong>de</strong> Janeiro, Rio <strong>de</strong> Janeiro, 22453-900, Brasil<br />
2 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, Rio <strong>de</strong> Janeiro, 21941-972,Brasil<br />
3 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral <strong>de</strong> Juiz <strong>de</strong> Fora, 36036-330, Brasil<br />
En<strong>de</strong>reço <strong>de</strong> e-mail do autor para correspondência: gms@vdg.fis.puc-rio.br<br />
Seções <strong>de</strong> choque absolutas para a perda<br />
eletrônica do projétil, a captura eletrônica<br />
pelo projétil e a ionização múltipla do alvo<br />
foram medidas em colisões entre íons <strong>de</strong> carbono<br />
triplamente ionizados e gases nobres,<br />
em função dos estados <strong>de</strong> carga finais do projétil<br />
e do alvo, para energias entre 1,3 e 3,5<br />
MeV [1]. Os dados foram comparados com<br />
outros resultados experimentais semelhantes<br />
existentes na literatura para diversos projéteis.<br />
Foram realizados cálculos a perda eletrônica<br />
simples do projétil acompanhada pela<br />
ionização múltipla do alvo para o modo <strong>de</strong><br />
blindagem (screening), usando tanto uma<br />
versão estendida do Mo<strong>de</strong>lo <strong>de</strong> Impulso Clássico<br />
<strong>de</strong> Colisões Livres (FCM) [2] quanto a<br />
Aproximação <strong>de</strong> Born <strong>de</strong> Ondas Planas (PW-<br />
BA), e para o modo <strong>de</strong> antiblindagem (antiscreening)<br />
<strong>de</strong>ntro da PWBA [3]. A <strong>de</strong>pendência<br />
do número <strong>de</strong> elétrons ativos para o antiscreening<br />
com a energia da colisão foi <strong>de</strong>scrita<br />
por uma função simples, que é “universal” no<br />
que diz respeito aos alvos, mas que, em princípio,<br />
<strong>de</strong>pen<strong>de</strong> do projétil consi<strong>de</strong>rado. Foi<br />
<strong>de</strong>senvolvido um método, <strong>de</strong>ntro da Aproximação<br />
<strong>de</strong> Impulso [4], para <strong>de</strong>terminar o número<br />
<strong>de</strong> elétrons ativos para o antiscreening<br />
em cada subcamada do alvo, no limite <strong>de</strong> altas<br />
velocida<strong>de</strong>s.<br />
No caso da captura eletrônica, a análise<br />
da <strong>de</strong>pendência dos processos <strong>de</strong> captura<br />
simples e <strong>de</strong> ionização com transferência com<br />
a carga do projétil mostrou que, no caso do<br />
alvo <strong>de</strong> He, projéteis <strong>de</strong>sprovidos <strong>de</strong> elétrons<br />
e projéteis carregando elétrons, mas com o<br />
mesmo estado <strong>de</strong> carga, apresentam seções <strong>de</strong><br />
choque muito semelhantes. Este fato indica<br />
que, nestes processos para o He, íons vestidos<br />
se comportam como partículas carregadas<br />
sem estrutura.<br />
Um comportamento semelhante ao da<br />
captura simples foi também observado na ionização<br />
simples pura do átomo <strong>de</strong> He por<br />
projéteis com diferentes estados <strong>de</strong> carga.<br />
Para os <strong>de</strong>mais gases nobres, este comportamento<br />
foi observado apenas para projéteis<br />
simplesmente carregados.<br />
Mostrou-se, ainda, que a <strong>de</strong>pendência<br />
das seções <strong>de</strong> choque <strong>de</strong> ionização simples<br />
pura do alvo com o quadrado da carga do<br />
projétil, predita por mo<strong>de</strong>los <strong>de</strong> primeira or<strong>de</strong>m,<br />
só é válida no regime <strong>de</strong> altas velocida<strong>de</strong>s.<br />
Para colisões mais lentas, a captura eletrônica<br />
pelo projétil se torna mais relevante e<br />
compete com a ionização simples pura do<br />
alvo. Tal fato se torna ainda mais importante<br />
à medida que a carga do projétil aumenta.<br />
Referências<br />
[1] A. C. F. Santos et al., Phys. Rev. A 82,<br />
012704 (2010).<br />
[2] G. M. Sigaud, J. Phys. B 41, 015205 (2008).<br />
[3] E. C. Montenegro e W. E. Meyerhof, Phys.<br />
Rev. A 43, 2289 (1991).<br />
[4] E. C. Montenegro e T. J. M. Zouros, Phys.<br />
Rev. A 50, 3186 (1994).<br />
50 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Prospects for a new synchrotron light source in Brazil<br />
Gustavo M. Azevedo 1<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Av. Bento Gonçalves 9500, Porto Alegre, Brasil<br />
corresponding author e-mail: gustavo.azevedo@ufrgs.br<br />
The Brazilian Synchrotron Light Source<br />
(LNLS) is in operation since 1997. More than a<br />
thousand scientists, mainly from Brazil and Latin<br />
America have open access to the LNLS facilities<br />
every year. Over the last 13 years, the storage<br />
ring and beam lines have been continuously<br />
improved and their operational parameters greatly<br />
overcame the originally planned performance.<br />
Worldwi<strong>de</strong>, remarkable advances in several scientific<br />
areas, such as structural molecular biology,<br />
nanotechnology and new materials were<br />
possible due to the wi<strong>de</strong>spread availability of<br />
synchrotron light sources. Many new facilities<br />
have been recently commissioned or upgra<strong>de</strong>d<br />
and new ones are being planned around the<br />
world.<br />
The LNLS storage ring is now reaching<br />
its physical limits for upgra<strong>de</strong>s and improvements.<br />
To keep competitiveness in this area, the<br />
LNLS Users community has pointed out the necessity<br />
of a new, high performance light source,<br />
with a brighter beam and broa<strong>de</strong>r energy range<br />
spectrum. In 2009, the <strong>de</strong>cision to build a new<br />
3 rd generation light source in Brazil was ma<strong>de</strong>.<br />
The project is now in its first stage (conceptual<br />
project) and its funding is in discussion with the<br />
Fe<strong>de</strong>ral Government and Science Funding<br />
Agencies.<br />
the following, some of the new possibilities<br />
opened up by the new facility in high resolution<br />
x-ray spectroscopy, x-ray scattering, timeresolved,<br />
in situ and in operando mo<strong>de</strong> experiments<br />
and experiments un<strong>de</strong>r extreme conditions<br />
will be illustrated. Finally, I will conclu<strong>de</strong><br />
presenting the conceptual project gui<strong>de</strong>lines,<br />
compare the expected performance parameters<br />
with existing and planned facilities<br />
around the world and present <strong>de</strong>tails on the construction<br />
costs and schedule.<br />
Figure 1. The LNLS experimental hall.<br />
In this talk, an overview of the history<br />
and current <strong>de</strong>velopment of Synchrotron Radiation<br />
Technology in Brazil will be presented. I<br />
will <strong>de</strong>tail the limitations of our light source,<br />
emphasizing the scientific challenges to be faced<br />
in the near future in important areas such as infectious<br />
and plant diseases (structural molecular<br />
biology), catalysis and oil industry, energy generation<br />
from “green” sources , geochemistry,<br />
environmental sciences and materials science. In<br />
51 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Quantum-mechanical and classical cross sections for ionization and capture<br />
induced by light ions on DNA and RNA nucleobases<br />
C. Champion 1 , H. Lekadir 1 , M. E. Galassi 2 , O. Fojón 2 , R. D. Rivarola 2 , and J. Hanssen 1<br />
1 Laboratoire <strong>de</strong> Physique Moléculaire et <strong>de</strong>s Collisions, Université Paul Verlaine-Metz, Metz, France<br />
2 Instituto <strong>de</strong> <strong>Física</strong> Rosario, CONICET, <strong>Universidad</strong> Nacional <strong>de</strong> Rosario, Rosario, Argentina<br />
Corresponding author: champion@univ-metz.fr<br />
DNA lesions and more particularly those<br />
involved in clustered damages are nowadays<br />
consi<strong>de</strong>red of prime importance for <strong>de</strong>scribing<br />
the post-irradiation cellular survival [1]. In<strong>de</strong>ed,<br />
these complex radio-damages may induce critical<br />
DNA lesions like double strand breaks<br />
whose relevance has been clearly i<strong>de</strong>ntified in<br />
the radio-induced cellular <strong>de</strong>ath process [2]. Un<strong>de</strong>r<br />
these conditions, further theoretical mo<strong>de</strong>ls<br />
as well as experimental data on ion-induced collisions<br />
at the DNA level remain still today crucial.<br />
Until recently, measurements on such biological<br />
systems remain scarce and are essentially<br />
limited to studies of mechanisms of radiation<br />
damage only explored at the mesoscopic scale<br />
and not at the single molecule (nanometric) one.<br />
In this context, ionization and fragmentation of<br />
isolated gas-phase nucleobases have received<br />
only little interest and were essentially focused<br />
on the cross section <strong>de</strong>termination for electroninduced<br />
collisions. Ion-induced collisions have<br />
rarely been reported in the literature and to the<br />
best of our knowledge, only few works exist.<br />
Thus, Schalthölter and co-workers have extensively<br />
studied the fragmentation mo<strong>de</strong>s induced<br />
by Xe q+ ions (q = 5-25) [3] and C q+ ions (q = 1-<br />
6) [4] on isolated nucleobases and more recently<br />
on nucleobase clusters [5]. Proton-induced collisions<br />
on DNA and RNA bases have been also<br />
experimentally investigated by many groups. Let<br />
us cite for example the work of Coupier et al. [6]<br />
where ionization and fragmentation of uracil<br />
molecules induced by protons were studied by<br />
means of coinci<strong>de</strong>nce techniques. More recently,<br />
Moretto-Capelle and co-workers have studied<br />
the ionization and fragmentation of isolated<br />
DNA/RNA bases and uridine nucleosi<strong>de</strong> induced<br />
by protons [7]. Finally, note that very recently<br />
Alvarado et al. [8] have studied collisions of<br />
slow light ions, namely, keV-H + , He 2+ and C +<br />
ions with DNA building blocks.<br />
On the theoretical si<strong>de</strong>, many attempts<br />
were proposed for predicting total ionization<br />
cross sections of simple biological molecules<br />
including DNA/RNA bases. Among them, we<br />
essentially find in the literature two major approaches<br />
<strong>de</strong>dicated to electron-induced collisions,<br />
namely, that proposed by Deutsch et al.<br />
[9] and commonly used by many groups and that<br />
based on the Binary-Encounter-Bethe (BEB)<br />
theory initially proposed by Kim and Rudd [10].<br />
Ion-induced collisions on DNA bases have been<br />
less studied and we essentially find two approaches<br />
in the literature: a first (semi)-classical<br />
one generally based on classical-trajectory<br />
Monte Carlo (CTMC) type approaches, and a<br />
second one <strong>de</strong>veloped in the quantummechanical<br />
framework and limited - for the major<br />
part of the existing studies - to the use of the<br />
first Born approximation. Let us first illustrate<br />
the “semi-classical group” by the study of Bacchus-Montabonel<br />
et al. [11] where C q+ (q = 2-4)<br />
induced collisions with uracil have been investigated<br />
pointing out the strong <strong>de</strong>pen<strong>de</strong>nce of the<br />
charge-transfer process with respect to the molecular<br />
target orientation. In the same kind of<br />
approach, we have recently applied a relatively<br />
simple classical mo<strong>de</strong>l which combines a homema<strong>de</strong><br />
CTMC co<strong>de</strong> with a classical over-barrier<br />
(COB) criteria to estimate the total cross sec-<br />
52 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
tions of single electron loss processes (capture<br />
and ionization) for collisions between multiply<br />
charged ions, namely, H + , He 2+ and C 6+ (with<br />
impact energies ranging from 10 keV/amu to<br />
10 MeV/amu) and DNA/RNA bases [12-13]. To<br />
the best of our knowledge the second group of<br />
“quantum mechanical approaches” is only represented<br />
by the recent work of Dal Cappello et al.<br />
[14] where differential and total ionization cross<br />
sections have been reported for protons impinging<br />
on cytosine molecules. However, the obtained<br />
total cross sections exhibited large discrepancies<br />
in magnitu<strong>de</strong> as well as in shape with<br />
our recent CTMC predictions [13], these later<br />
showing nevertheless a very good agreement<br />
with semi-classical results obtained by using the<br />
simple Rutherford formula proposed by Stolterfoht<br />
et al. [15].<br />
In the present work, quantum-mechanical<br />
and classical calculations of doubly and singly<br />
differential as well as total cross sections are<br />
presented for ionization and capture processes<br />
induced by proton, α-particle and bare ion<br />
carbon beams impacting on a<strong>de</strong>nine, cytosine,<br />
thymine and guanine bases.<br />
TCS (10 -16 cm 2 )<br />
1 0 2<br />
1 0 1<br />
1 0 0<br />
C B 1<br />
1 0 -1<br />
a ) H +<br />
+ A d e n in e<br />
C D W - E IS<br />
C T M C - C O B<br />
e x p e r im e n ta l<br />
1 0 2 c ) H + + T h ym in e<br />
b ) H +<br />
+ C y to s in e<br />
d ) H +<br />
+ G u a n in e<br />
References<br />
[1] A. Yokoya et al., Radiat. Phys. Chem. 77,<br />
1280 (2008).<br />
[2] H. Nikjoo and L. Lindborg, Phys. Med. Biol.<br />
55, R65 (2010).<br />
[3] J. <strong>de</strong> Vries et al., Phys. Rev. Lett. 91, 053401<br />
(2003).<br />
[4] J. <strong>de</strong> Vries et al., Eur. Phys. J. D 24, 161<br />
(2003).<br />
[5] T. Schlathölter et al., Chem. Phys. Chem. 7,<br />
2339 (2006).<br />
[6] B. Coupier et al., Eur. Phys. J. D 20, 459<br />
(2002).<br />
[7] A. Le Pa<strong>de</strong>llec et al., J. Phys: Conf. Series<br />
101, 012007 (2008).<br />
[8] F. Alvadaro et al., J. Chem. Phys. 127,<br />
034301 (2007).<br />
[9] H. Deutsch et al., Int. J. Mass. Spectrom.<br />
197, 37 (2000).<br />
[10] Y. K. Kim and M. E. Rudd, Phys. Rev. A<br />
50, 3954 (1994).<br />
[11] M. C. Bacchus-Montabonel et al., Phys.<br />
Rev. A 72, 052706 (2005).<br />
[12] I. Abbas et al., Phys. Med. Biol. 53, N41<br />
(2008).<br />
[13] H. Lekadir et al., Phys. Rev. A 79, 062710.<br />
[14] C. Dal Cappello et al., Phys. Rev. A 78,<br />
042702 (2008).<br />
[15] N. Stolterforht, R. D. DuBois and R. D.<br />
Rivarola in Electron emission in heavy ion-atom<br />
collisions, edited by G. Ecker, P. Lambropoulos,<br />
I. I. Sobel’man, and H. Walther (Springer series<br />
on Atoms and Plasma, Berlin, 1997).<br />
1 0 1<br />
1 0 0<br />
1 0 -1<br />
1 0 1 1 0 2 1 0 3 1 0 4 1 0 15<br />
1 0 2 1 0 3 1 0 4 1 0 5<br />
In c id e n t p ro to n e n e rg y (k e V /u )<br />
Figure 1. Total ionization cross sections (10 -16 cm 2 )<br />
for the four DNA bases here investigated, namely,<br />
a<strong>de</strong>nine (panel a), cytosine (panel b), thymine (panel<br />
c), and guanine (panel d) impacted by protons.<br />
53 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Secondary Ions emission from Alkanethiol-SAMs due to highly charged ions<br />
bombardment<br />
M Flores 1 , V. Esaulov 2 and Y. Yamazaki 3<br />
1 Depto. <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> ciencias físicas y matemáticas, <strong>Universidad</strong> <strong>de</strong> Chile, casilla 110-V, Santiago, Chile.<br />
2 Laboratoire <strong>de</strong>s Collisions Atomiques et Moleculaires, Universite Paris-Sud, Orsay Ce<strong>de</strong>x, France.<br />
3 Atomic Physics Laboratory, Riken Institute, Wako, Saitama, Japan.<br />
email address corresponding author: mflorescarra@ing.uchile.cl<br />
Self-assembled monolayers (SAMs) are<br />
or<strong>de</strong>red molecular assemblies formed by the adsorption<br />
of an active surfactant on a solid surface.<br />
SAMs provi<strong>de</strong> a convenient, flexible, and<br />
simple system with which to tailor the interfacial<br />
properties of metal, metal oxi<strong>de</strong>s and semiconductors<br />
[1]. The alkanethiols are a common type<br />
of molecules used to build SAMs.<br />
Several techniques have been used to<br />
study and characterize SAMs, for example SPM,<br />
optical and ion spectroscopies. In the latter case,<br />
the interaction of ions with SAM surfaces leads<br />
to the sputtering of molecules from the surface,<br />
with the <strong>de</strong>tection of such molecules giving information<br />
on both the chemical and structural<br />
composition of the SAM. For this reason much<br />
experimental and theoretical effort has been directed<br />
towards ion-SAM collisions. Special case<br />
is the highly charged ions (HCI).<br />
For slow HCI, the potential energy stored<br />
in the projectile can far exceed its kinetic energy.<br />
In contrast to the kinetic sputtering process,<br />
which is due to momentum transfer from the<br />
ion to the surface, HCI may also transfer significant<br />
potential energy, removing ions and molecules<br />
from the surface in a process called potential<br />
sputtering.<br />
SAMs of the alkanethiol molecules Un<strong>de</strong>canethiol<br />
(UDT), HS(CH 2 ) 10 CH 3 , and Do<strong>de</strong>canethiol<br />
(DDT), HS(CH 2 ) 11 CH 3 , were prepared<br />
on atomically flat Au(111) which was <strong>de</strong>posited<br />
as a thin film on freshly cleaved mica.<br />
The quality of the SAMs was confirmed by<br />
STM observations [2]. The samples were bombardment<br />
with Ar q+ ions.<br />
The q-<strong>de</strong>pen<strong>de</strong>nce of the proton sputtering<br />
yield from hydrogen contaminated/covered surfaces<br />
has been found to follow a power law <strong>de</strong>pen<strong>de</strong>nce<br />
and this was explained by the classical<br />
over barrier mo<strong>de</strong>l. In this mo<strong>de</strong>l a HCI approaching<br />
an atom/molecule induces multielectron<br />
transfer. In the case of our SAM it<br />
would induce electron transfer from the alkanethiol<br />
molecule terminal functional group.<br />
Removal of two electrons from the most external<br />
part of the SAM, would create a doubly charged<br />
chemical bond (C-H) 2+ . Because the molecule is<br />
a poor conductor, the reneutralization probability<br />
in the molecular layer should be lower than<br />
on a metal, and a proton may be released in the<br />
bond direction by Coulomb repulsion [3]. In<br />
general, in the above mo<strong>de</strong>l the proton yield is<br />
then <strong>de</strong>pen<strong>de</strong>nt on the probabilities of removal<br />
of the first and second electron and on reneutralization<br />
as the ion moves away from the surface,<br />
given a power law, Fig 1(a,b), and in the<br />
case un<strong>de</strong>r study the probabilities are strong <strong>de</strong>pen<strong>de</strong>nt<br />
of the orientation of the terminal functional<br />
group, Fig. 1(c,d).<br />
Figure 1. Proton Yields from (a)UDT and (b)DDT<br />
un<strong>de</strong>r bombardment with Ar q+ ions. Top surface<br />
scheme of the SAMs corresponding to (c)UDT and<br />
(d)DDT.<br />
References<br />
[1] Love et al, Chem. Rev. 105 (2005) 1103.<br />
[2] O’Rourke et al, Appl. Phys. Lett., submitted.<br />
[3] Flores et al, Phys. Rev. A79 (2009) 022902.<br />
54 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Structural characterization of Pb nanoislands in SiO 2 /Si interface synthesized<br />
by ion implantation through MEIS analysis<br />
D. F. Sanchez 1 , F. P. Luce 2 , Z. E. Fabrim 1 , M. A. Sortica 1 , P. F. P. Fichtner 1 and P. L.<br />
Gran<strong>de</strong> 1<br />
1 Institute of Physics, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Porto Alegre, Brazil<br />
email address corresponding author: dario.f.sanchez@gmail.com<br />
Recently, the Medium Energy Ion Scattering<br />
(MEIS) technique has been used as an<br />
additional tool for characterization of<br />
nanoparticles (NPs), where basically their<br />
shape, composition, size distribution,<br />
stoichiometry and the <strong>de</strong>termination of <strong>de</strong>pth<br />
distributions of different elements in a single<br />
NP have been successfully obtained. We have<br />
<strong>de</strong>veloped a Monte Carlo simulation and fitting<br />
software, the PowerMeis [1], that consi<strong>de</strong>rs<br />
any geometry, size distribution, <strong>de</strong>nsity<br />
of the nanostructures and also the asymmetry<br />
of the energy loss-distribution. In this<br />
work we investigate buried Pb NPs synthesized<br />
by ion implantation on SiO 2 /Si thin<br />
film, with low temperature and long aging<br />
time treatments followed by a high temperature<br />
thermal annealing. This process [2] leads<br />
to the formation of a <strong>de</strong>nse 2D NPs array located<br />
at the SiO 2 /Si interface, as shown in<br />
Fig. 1. Through the 2D MEIS spectra (energy<br />
and angle), we have studied the nanostructure<br />
geometry, number <strong>de</strong>nsity and mean NP size<br />
of such system. The present results are compared<br />
to transmission electron microscopy<br />
(TEM) measurements.<br />
Figure 1. (a) HRTEM micrograph from a [011] oriented<br />
sample presenting a cross-section view of the<br />
NPs partially embed<strong>de</strong>d in the Si matrix; (b) Brightfield<br />
two-beam image, un<strong>de</strong>rfocus, <strong>de</strong>monstrating<br />
that the NPs are exclusively located at the SiO 2 /Si<br />
(100) interface. (c) Plan-view image (bright field, in<br />
focus) close to the (001) zone axis, showing square<br />
based NPs preferentially aligned parallel to the (011)<br />
planes of the matrix.<br />
In Fig. 2 is compared the experimental<br />
MEIS spectra to the simulation performed by<br />
the PowerMeis software using the NP geometrical<br />
shape <strong>de</strong>scribed in Fig. 3 and number<br />
<strong>de</strong>nsity of 3.5×10 11 cm -2 , close to<br />
55 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
3.75×10 11 cm -2 , the value from the TEM planview<br />
images.<br />
images can be also observed that the PF<br />
shape is in better agreement.<br />
Figure 2. Experimental and simulated 2D MEIS<br />
spectra.<br />
To investigate the geometrical shape of<br />
the NPs, the system was mo<strong>de</strong>lled in two different<br />
ways: i) as a hemisphere in the SiO 2<br />
si<strong>de</strong> on a pyramidal frustum in the Si matrix<br />
si<strong>de</strong> (further referred as PF) and ii) as a<br />
sphere, half in the SiO 2 and half in the Si matrix.<br />
The parameters of the PF shape are <strong>de</strong>scribed<br />
in Fig. 3 and the variable parameter<br />
of the spherical shape is the radius.<br />
To <strong>de</strong>terminate the size and number<br />
<strong>de</strong>nsity of NPs, it were performed simulations<br />
with several number <strong>de</strong>nsities for booth<br />
geometrical mo<strong>de</strong>ls, and their the radius was<br />
adjusted in or<strong>de</strong>r to keep the same Pb per<br />
area, namely (Nt) Pb,MEIS = 2.26×10 15 atoms∙cm<br />
-2 , value obtained by the MEIS measurement,<br />
which is close to the one obtained<br />
by auxiliary RBS measurements. The number<br />
<strong>de</strong>nsity obtained for the PF shape is<br />
(4.2±1.6)×10 11 cm -2 , and, (5.3±1.7)×10 11 cm -2<br />
consi<strong>de</strong>ring the spherical shape. These values<br />
of <strong>de</strong>nsities correspond to the values of radii<br />
of (3.7±0.5)nm for PF shape and (3.2±0.4)nm<br />
for spherical shape. The result for PF shape<br />
agrees better to the value obtained by TEM,<br />
namely radius of (4±1) nm and number <strong>de</strong>nsity<br />
of 3.7×10 11 cm -2 . Through the HRTEM<br />
Figure 2. The PF geometrical shape mo<strong>de</strong>l is <strong>de</strong>scribed<br />
by three parameters: the radius, the angle θ<br />
and the <strong>de</strong>pth h. The NPs anisotropy observed in the<br />
TEM micrographs was taken into account, and is<br />
related to (110) and (010) Si plane direction. Above,<br />
(a) a lateral perspective at (110) and (c) (010) direction<br />
of Si substrate, (b) seen from above and (d) from<br />
below.<br />
Here we have shown the capability of<br />
MEIS analysis to characterize buried NPs,<br />
which opens new perspectives for nanostructure<br />
analysis in situ that can be of great interest.<br />
References<br />
[1] M. A. Sortica, P. L. Gran<strong>de</strong>, G. Machado, L.<br />
Miotti, Journal of Applied Physics 106, 114320<br />
(2009).<br />
[2] F. Kremer, J. M. J. Lopes, F. C. Zawislak,<br />
and P. F. P. Fichtner, Appl. Phys. Lett. 91,<br />
083102 (2007).<br />
56 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Supression of binary and recoil peaks in ionization of H 2 by electron impact<br />
Fojón O A, Stia C R and Rivarola R D<br />
Instituto <strong>de</strong> <strong>Física</strong> Rosario (CONICET-UNR), Pellegrini 250 (2000) Rosario, Argentina<br />
email address corresponding author: fojon@ifir-conicet.gov.ar<br />
We study theoretically the single<br />
ionization of H 2 molecules by fast electron<br />
impact. Our aim is to show that interferences<br />
coming from the coherent emission from the<br />
molecular centers may produce unexpected<br />
consequences in the physical features of the<br />
observables of the reaction.<br />
Interference phenomena have been of<br />
crucial importance in the foundation of quantum<br />
mechanics. Analogies with the Young two-slit<br />
experiment played a fundamental role in the<br />
<strong>de</strong>scription and comprehension of the dual<br />
nature of quantum objects such as electrons. A<br />
fascinating alternative way of observing<br />
interference patterns is provi<strong>de</strong>d by the electron<br />
spectra resulting from the ionization of<br />
molecular diatomic targets. In the sixties, it was<br />
suggested that the coherent emission from these<br />
molecules may give rise to specific oscillations<br />
in the differential cross sections of the ejected<br />
electrons, the two molecular centers acting as the<br />
analogues of the two slits in the Young<br />
experiment [1]. However, this kind of<br />
oscillations was measured for the very first time<br />
with fast krypton ions impacting on H 2 [2]. In<br />
previous works, we have shown that these<br />
interference patterns may be observed also for<br />
electron impact [3-7].<br />
We focus here on electron emission at<br />
high impact energies from fixed-in-space H 2<br />
molecules impacted by fast electrons. We study<br />
transitions at fixed equilibrium internuclear<br />
distance from the ground state of H 2 to the<br />
ground (gera<strong>de</strong>) and first excited (ungera<strong>de</strong>)<br />
state of the H +<br />
2 residual target. We consi<strong>de</strong>r<br />
coplanar geometries in which the inci<strong>de</strong>nt,<br />
scattered and ejected momenta lie all in the same<br />
plane. In addition, we analyze asymmetric<br />
kinematics situations in which one slow and one<br />
fast electron are <strong>de</strong>tected in the final channel.<br />
We employ a first or<strong>de</strong>r mo<strong>de</strong>l obtained<br />
in the framework of a two-effective center<br />
approximation (TEC). The i<strong>de</strong>a exploited in the<br />
TEC mo<strong>de</strong>l is that although electrons in the<br />
ground state of H 2 are shared by both nuclei, the<br />
electronic <strong>de</strong>nsity is peaked at the nuclei<br />
positions. Then, it is argued that ejection occurs<br />
in the neighbourhoods of one nucleus while the<br />
nuclear charge of the other one is screened<br />
completely by the non ionized electron.<br />
Consequently, a unique final effective<br />
continuum function satisfying the correct<br />
asymptotic long range conditions is used to<br />
represent the ejected electron in the final channel<br />
of the reaction. This mo<strong>de</strong>l gives reasonably<br />
good agreement with experiments [8]<br />
constituting thus a good approximation to the<br />
final state of the reaction in which three charged<br />
bodies interact through Coulomb potentials. In<br />
or<strong>de</strong>r to take into account the complexities of<br />
this interaction in an approximate way, one can<br />
take a more elaborated final function such as the<br />
one used in Ref. [9]. This function <strong>de</strong>scribes the<br />
final interactions through a product of three<br />
Coulomb functions associated to the three twobody<br />
pairs present in the final channel. The<br />
approximation obtained using this function for<br />
molecular targets gives an excellent agreement<br />
with experiments [10].<br />
We show here for the first time that un<strong>de</strong>r<br />
<strong>de</strong>finite conditions, <strong>de</strong>structive interferences<br />
coming from the coherent emission from both<br />
molecular centers provoke the supression of the<br />
binary peak in the multiple differential cross<br />
sections corresponding to transitions leading to<br />
final ground state of H 2 + . This is a surprising<br />
result as is well known that ejection is classically<br />
more likely to be produced in the binary region.<br />
Moreover, this finding is shocking as so far and<br />
up to our knowledge the presence of the binary<br />
peak was assumed for every ionization reaction<br />
with either atomic or molecular targets [11].<br />
57 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Nonetheless, we <strong>de</strong>monstrate proceeding further<br />
that not only the binary but also the recoil peak<br />
may be supressed when transitions involve the<br />
first excited (ungera<strong>de</strong>) state of the residual<br />
target. A similar effect was discovered for<br />
emission of photoelectrons: at <strong>de</strong>finite photon<br />
energies, electron ejection in the classical<br />
direction given by the polarization vector is<br />
forbid<strong>de</strong>n for molecules aligned with the<br />
polarization vector [12,13].<br />
Unfortunately, no experiments with<br />
oriented molecules are available at present to<br />
contrast with our predictions. Notwithstanding,<br />
in the age of the COLTRIMS and reaction<br />
microscopes [14] is possible to envisage in the<br />
near future the coming of experimental work to<br />
corroborate (or not) our findings.<br />
[11] O. Al-Hagan et al, Nature Physics 5, 59<br />
(2009).<br />
[12] J. Fernán<strong>de</strong>z, O. Fojón, A. Palacios and F.<br />
Martín, Phys. Rev. Lett. 98, 043005 (2007).<br />
[13] J. Fernán<strong>de</strong>z, O. Fojón and F. Martín, Phys.<br />
Rev. A 79, 023420 (2009).<br />
[14] Ten years of COLTRIMS and reaction<br />
microscopes, collection of papers edited by J.<br />
Ullrich, Max Planck Institute für Kernphysik<br />
Hei<strong>de</strong>lberg (2004).<br />
References<br />
[1] H. D. Cohen and U. Fano, Phys. Rev. 150,<br />
30 (1966).<br />
[2] N. Stolterfoht et al, Phys. Rev. Lett. 87,<br />
023201 (2001).<br />
[3] C. R. Stia, O. A. Fojón, P. Weck, J. Hanssen,<br />
and R. D. Rivarola, J. Phys. B: At. Mol. Opt.<br />
Phys. 36, L257 (2003).<br />
[4] O. Kamalou, J.-Y. Chesnel, D. Martina, F.<br />
Frémont, J. Hanssen, C. R. Stia, O. A. Fojón, R.<br />
D. Rivarola, Phys. Rev. A 71, 010702(R)<br />
(2005).<br />
[5] S. Chatterjee, D. Misra, A. H. Kelkar, L.<br />
Tribedi, C. R. Stia, O. A. Fojón and R. D.<br />
Rivarola, Phys. Rev. A 78, 052701 (2008).<br />
[6] S. Chatterjee, S. Kasthurirangan, A. H.<br />
Kelkar, C. R. Stia, O. A. Fojón, R. D. Rivarola<br />
and L. Tribedi, J. Phys. B: At. Mol. Opt. Phys.<br />
42, 065201 (2009).<br />
[7] S. Chatterjee, A. N. Agnihotri, C. R. Stia, O.<br />
A. Fojón, R. D. Rivarola and L. Tribedi, Phys.<br />
Rev. A (2010) in press.<br />
[8] P. Weck, O. A. Fojón, J. Hanssen, B.<br />
Joulakian and R. D. Rivarola, Phys. Rev. A 63,<br />
042709 (2001).<br />
[9] M. Brauner, J. S. Briggs and H. Klar, J.<br />
Phys. B: At. Mol. Opt. Phys. 22, 2265 (1989).<br />
[10] C. R. Stia, O. A. Fojón, Ph. Weck, J.<br />
Hanssen, B. Joulakian and R. D. Rivarola, Phys.<br />
Rev. A 66, 052709 (2002).<br />
58 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
The role of electronic excitations in the energy loss of hydrogen clusters in<br />
dielectric and metallic materials<br />
S. M. Shubeita 1 , R. C. Fadanelli 1 , J. F. Dias 1 , P. L. Gran<strong>de</strong> 1 , C. D. Denton 2 , I. Abril 2 ,<br />
R. Garcia-Molina 3 and N. R. Arista 4<br />
1 Instituto <strong>de</strong> <strong>Física</strong> da Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Porto Alegre, RS, Brazil<br />
2 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong> Aplicada, <strong>Universidad</strong> d’Alicante, Alicante, Spain<br />
3 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong> – CIOyN, <strong>Universidad</strong> <strong>de</strong> Murcia, Murcia, Spain<br />
4 Centro Atômico Bariloche, Instituto Balseiro, San Carlos <strong>de</strong> Bariloche, Rio Negro, Argentina<br />
e-mail address corresponding author: samir.shubeita@ufrgs.br<br />
The aim of this work is to study the<br />
signature of plasmon excitations induced by<br />
H + 2 and H + 3 ionic clusters when interacting<br />
with thin (10-50 Å) layers of dielectric<br />
(SiO 2 , LaScO 3 , HfO 2 ) and metallic (Au)<br />
materials. For this purpose, high energy<br />
resolution backscattering experiments were<br />
carried out as a function of the incoming<br />
projectile energy, covering an energy range<br />
between 40 and 200 keV/nucleon. The ratio<br />
R n between the energy loss of the cluster and<br />
the sum of the energy loss of its constituents<br />
provi<strong>de</strong>s the information about the plasmon<br />
excitation threshold, which is characteristic<br />
for each material. The results obtained for<br />
the high-k dielectrics (LaScO 3 and HfO 2 )<br />
and Au do not show any clear evi<strong>de</strong>nce of<br />
plasmon excitations induced by H +<br />
2 ionic<br />
clusters (see fig. 1 for HfO 2 ). These results<br />
are supported by calculations based on the<br />
dielectric formalism. However, for the SiO 2<br />
thin film (fig. 2), the plasmon excitation<br />
threshold is observed at about 70<br />
keV/nucleon for both cluster ions (H + 2 and<br />
H + 3 ) [1]. In fact, unlike SiO 2 where a dominant<br />
long-range electronic excitation is present,<br />
the HfO 2 , LaScO 3 and Au have several<br />
and equally important excitation energies<br />
(mix of plasmon excitations, excitons and<br />
interband transitions). They lead to different<br />
onset projectile-energies, which explains the<br />
smoothly increase of stopping ratio [2].<br />
Also, the results obtained for Au are compared<br />
with previous results [3].<br />
Figure 1. The experimental energy loss ratio R 2<br />
(squares) for HfO 2 as a function of the inci<strong>de</strong>nt cluster<br />
energy, in comparison with different theoretical<br />
approaches.<br />
Figure 2. The experimental stopping ratio R 2 (full<br />
squares) as a function of the inci<strong>de</strong>nt H +<br />
2 cluster<br />
energy. The thick lines represent the dielectric formalism<br />
calculations including plasmon excitations<br />
(full line) and without plasmon excitations (dotted<br />
lines) after averaging over charge-state fractions of<br />
H + and H 0 .<br />
59 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
References<br />
[1] S. M. Shubeita, M. A. Sortica, P. L. Gran<strong>de</strong>,<br />
J. F. Dias and N. R. Arista, Phys. Rev. B 77,<br />
115327 (2008).<br />
[2] S. M. Shubeita, R. C. Fadanelli, J. F. Dias, P.<br />
L. Gran<strong>de</strong>, C. D. Denton, I. Abril, R. Garcia-<br />
Molina and N. R. Arista, Phys. Rev. B 80,<br />
205316 (2009).<br />
[3] W. Brandt, A. Ratkowski and R. H. Ritchie,<br />
Phys. Rev. Lett. 33, 1325 (1974).<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Contribuciones - Paneles<br />
Título<br />
Autores<br />
P1<br />
Electron emission by grazing scattering from<br />
Be(0001)<br />
C. D. Archubi, M. S. Gravielle and V. M.<br />
Silkin<br />
Claudio D. Archubi<br />
P2<br />
Monte Carlo simulation for proton track<br />
structure in biological matter<br />
H. Lekadir, C. Champion, S. Incerti, M. E.<br />
Galassi, O. Fojón, R. D. Rivarola, and J.<br />
Hanssen<br />
Christophe . Champion<br />
P3<br />
P4<br />
P5<br />
P6<br />
Multiple differential cross sections for the<br />
ionization from the 1B1 orbital of liquid water<br />
molecule by fast electron impact<br />
M.L. <strong>de</strong> Sanctis, O. Fojón, C. Stia, R.<br />
Vuilleumier and M.-F. Politis<br />
M.L. <strong>de</strong> Sanctis<br />
L. Sigaud, Natalia Ferreira, V.L.B. <strong>de</strong> Jesus,<br />
I<strong>de</strong>ntificação dos caminhos <strong>de</strong> fragmentação da W. Wolff, A.L.F. <strong>de</strong> Barros, A.C.F. dos<br />
Lucas Sigaud<br />
molécula <strong>de</strong> CHClF2 quando ionizada por elétrons Santos, R.S. Menezes, A.B. Rocha, M.B.<br />
Shah, E.C. Montenegro<br />
Rafaela Debastiani, Carla Eliete Iochims<br />
dos Santos, Liana Appel Boufleur,<br />
Café Brasileiro: Estudo da Concentração Masahiro Hatori, Débora Elisa Peretti,<br />
Rafaela Debastiani<br />
Elementar Utilizando Feixes Iônicos<br />
Vanessa Sobrosa Souza, Mateus Maciel<br />
Ramos, Elis Moura Stori, Cláudia Telles <strong>de</strong><br />
Souza, Livio Amaral, Johnny Ferraz Dias<br />
Coherencia y localización parcial en emisión<br />
electrónica simple <strong>de</strong> moléculas diatómicas<br />
moléculas diatómicas<br />
C. Tachino, M. Galassi, F. Martín, y R.<br />
Rivarola<br />
Roberto Rivarola<br />
P7<br />
P8<br />
P9<br />
Estados selectivos <strong>de</strong> captura <strong>de</strong> electrones en<br />
colisiones <strong>de</strong> 3He2++He a energías intermedias<br />
<strong>de</strong> impacto aplicando la técnica COLTRIMS<br />
Estudio <strong>de</strong> colisiones con proyectiles neutros y<br />
cargados sobre blancos moleculares <strong>de</strong> H2 a<br />
energías intermedias <strong>de</strong> impacto con la técnica<br />
COLTRIMS<br />
Doble Ionización <strong>de</strong> Helio por impacto <strong>de</strong> iones:<br />
Influencia <strong>de</strong> la Carga <strong>de</strong>l Proyectil<br />
M. Alessi, S. Otranto, D. Fregenal, P. Focke Mariana Alessi<br />
M. Alessi, D. Fregenal, P. Focke Mariana Alessi<br />
S. D. López, S. Otranto, C. R. Garibotti S. López<br />
61 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
P10<br />
Lα, Lβ, and Lγ x-ray production cross sections<br />
of Sm, Dy, Ho, and Tm by electron impact.<br />
Distorted-wave calculations vs experiment<br />
José M. Fernán<strong>de</strong>z-Varea, Silvina Segui<br />
and Michael Dingfel<strong>de</strong>r<br />
José M. Fernán<strong>de</strong>z-Varea<br />
P11<br />
Estudio <strong>de</strong> po<strong>de</strong>r <strong>de</strong> frenado <strong>de</strong> partículas α en<br />
películas <strong>de</strong>lgadas <strong>de</strong> cobre en el intervalo <strong>de</strong><br />
energía entre 1,0 a 2,0 MeV.<br />
Roberto Hauyón, German Kremer, Pedro<br />
Miranda y J. Roberto Morales<br />
Roberto Hauyón<br />
P12<br />
Ab-Initio Sturmian method for three-body A. L. Frapiccini, J. M. Randazzo, G.<br />
quantum mechanical problems: Scattering states Gasaneo, F. D. Colavecchia, D. M. Mitnik<br />
and ionizing collisions<br />
and L. U. Ancarani<br />
Darío M. Mitnik<br />
P13<br />
Ionización <strong>de</strong> hidrógeno atómico e iones<br />
moleculares H+2 por pulsos láser<br />
R. <strong>de</strong>lla Picca, J. Fiol, P. D. Fainstein Juan Fiol<br />
P14<br />
Un mo<strong>de</strong>lo <strong>de</strong> onda distorsionada para ionización<br />
electrónica en colisiones entre iones vestidos y<br />
blancos atómicos<br />
J. M. Monti, P. D. Fainstein , R. D. Rivarola Roberto D. Rivarola<br />
P15<br />
Canalización cuasiplanar <strong>de</strong> protones<br />
energéticos en inci<strong>de</strong>ncia normal sobre<br />
nanotubos <strong>de</strong> carbono <strong>de</strong> pared múltiple<br />
Jorge E. Valdés, Isabel Abril, Cristian D.<br />
Denton, P. Vargas, E. Figueroa, Néstor R.<br />
Arista, Rafael Garcia-Molina<br />
Isabel Abril<br />
P16<br />
Bulk plasmon excitation in grazing inci<strong>de</strong>nce<br />
ionmetal surface collisions<br />
C.A. Salas , F.A. Gutierrez and H. Jouin<br />
C.A. Salas<br />
P17<br />
Distribuciones <strong>de</strong> Scattering Multiple y Efectos<br />
Angulares en la Pérdida <strong>de</strong> energía <strong>de</strong> Protones<br />
y Deuterones en Láminas Delgadas <strong>de</strong> Carbono<br />
Amorfo<br />
E. D. Cantero, G. H. Lantschner1, N. R.<br />
Arista<br />
Esteban D. Cantero<br />
P18 Stopping power y Straggling <strong>de</strong> protones en Pd<br />
P. A. Miranda, A. Sepúlveda, E. Burgos, H.<br />
Fernán<strong>de</strong>z, J. R. Morales<br />
A. Sepúlveda<br />
P19<br />
Energy Loss of slow Hydrogen and Helium ions in<br />
channeling conditions in Au single crystal<br />
A.M. Calle, J.D. Uribe, C. Celedón, E.A.<br />
Figueroa, J.E. Valdés.<br />
Juan Uribe<br />
P20<br />
Pérdida <strong>de</strong> energía <strong>de</strong> protones en láminas<br />
<strong>de</strong>lgadas <strong>de</strong> Carbono amorfo.<br />
C. Celedón, J. E. Valdés, P. Vargas, E.<br />
Figueroa<br />
Carlos Celedón<br />
62 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
P21<br />
Energy losses of H and F ions in grazing<br />
scattering on a missing row reconstructed<br />
Au(110) surface<br />
Lin Chen, J.E. Valdés, P. Vargas, Jie Shen,<br />
V.Esaulov<br />
Jorge E. Valdés<br />
P22<br />
Inverse photoemission espectroscopy on<br />
graphene.<br />
V. Del Campo, P. Häberle Valeria Del Campo<br />
P23<br />
Elemental analysis of the Chaitén volcano ash<br />
2008-2009 eruptions<br />
Shimrit Elimelech, Jorge E. Valdés and<br />
Patricio Vargas<br />
Shimrit Elimelech<br />
Múltipla ionização <strong>de</strong> Neônio em coincidência W. Wolff, H. M. R. <strong>de</strong> Luna, A.C. F. dos<br />
P24 com íons <strong>de</strong> B2+ no regime <strong>de</strong> energia <strong>de</strong> poucos Santos, e E. C. Montenegro, G.M. Sigaud,<br />
MeV<br />
C.C.Montanari, e J.E.Miraglia<br />
Wania Wolff<br />
63 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
64 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Electron emission by grazing scattering from Be(0001)<br />
C. D. Archubi 1 , M. S. Gravielle 1,2 and V. M. Silkin 3,4<br />
1 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio, CONICET-UBA, Buenos Aires, Argentina<br />
2 Depto. <strong>de</strong> <strong>Física</strong>, Fac. <strong>de</strong> C. Exactas y Naturales, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Buenos Aires, Argentina<br />
3 Donostia Internacional Physics Center (DIPC), 20018, San Sebastián, Spain<br />
4 IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain<br />
email address corresponding author: archubi@iafe.uba.ar<br />
1. INTRODUCTION<br />
Recently it has been <strong>de</strong>monstrated that<br />
occupied surface states can modify the dielectric<br />
properties of metal surfaces [1]. Thus, with the<br />
aim of investigating the influence of surface<br />
states on electron emission, we study electron<br />
distributions originated by fast protons colliding<br />
grazing with a Be(0001) surface. Beryllium presents<br />
a technological interest in mo<strong>de</strong>rn fusion<br />
reactors and it is expected that its surface states<br />
play an important role in inelastic electronic<br />
processes.<br />
To <strong>de</strong>scribe the electron emission process<br />
we employ the Band-structure-based (BSB)<br />
mo<strong>de</strong>l [2], which inclu<strong>de</strong>s an accurate <strong>de</strong>scription<br />
of the electron-surface potential, incorporating<br />
information about the band structure of the<br />
solid. Within the BSB approach the surface interaction<br />
is <strong>de</strong>scribed by a realistic onedimensional<br />
mo<strong>de</strong>l potential [3], while the dynamic<br />
response of the medium is <strong>de</strong>rived in consistent<br />
way from the unperturbed electronic<br />
states by using a linear response theory. This<br />
method has been succesfully employed to study<br />
energy loss and electron emission from Al surfaces,<br />
where the effects of the surface states<br />
were found negligible [4].<br />
2. RESULTS<br />
Due to the large mass of the projectile, it<br />
is reasonable to calculate its motion in terms of a<br />
classical trajectory. Within the binary collisional<br />
formalism, the transition probability per unit<br />
path reads<br />
dP 2 π<br />
( x)<br />
= δ ( ∆)<br />
T<br />
dk vs<br />
if<br />
2<br />
(1)<br />
where z is the projectile distance to the surface,<br />
v s is the projectile velocity parallel to the surface<br />
plane, and the Dirac <strong>de</strong>lta expresses the<br />
energy conservation. In Eq (1) T if represents the<br />
T-matrix element, which is evaluated within a<br />
first-or<strong>de</strong>r-perturbation theory.<br />
In this work we employ the BSB mo<strong>de</strong>l<br />
to <strong>de</strong>rive both the unperturbed electronic wave<br />
functions and the surface induced potential. The<br />
differential probability of electron transition to a<br />
<br />
given final state with momentum k , is dP dk<br />
, obtained<br />
from Eq (1) by integrating along the classical<br />
projectile trajectory, after adding the contributions<br />
coming from the different initial<br />
states.<br />
10 1<br />
10 0<br />
10 -1<br />
dP/dk (a.u.)<br />
dP/dk (a.u.)<br />
10 -2<br />
10 -3<br />
10 -4<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
10 -3<br />
10 -4<br />
100 100 keV keV H + H + Be Be (0001)<br />
α = 1<br />
α = 1 ο ο<br />
30 60 90 120 150 180 210 240<br />
30 60 90 120 150 180 210 240<br />
Energy (eV)<br />
Energy (eV)<br />
θ=20 ο<br />
θ=20 ο<br />
θ=30 ο<br />
θ=30 ο<br />
θ=45 ο<br />
θ=45 ο<br />
θ=30 ο Jellium<br />
Figure 1. Differential probability of electron emission<br />
from the valence band, as a function of the electron<br />
energy, for 100 keV protons impinging on a Be<br />
(0001) surface with the angle α=1 o . Three different<br />
electron emission angles, meassured with respect to<br />
the surface plane, are consi<strong>de</strong>red: θ =20, 30 and 45<br />
o .<br />
65 Valparaíso, Chile
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In Fig. 1 we display the differential electron<br />
emission probability for 100 keV protons<br />
impinging grazing on a Be (0001) surface consi<strong>de</strong>ring<br />
three different ejection angles in the<br />
scattering plane. Due to the contribution of surface<br />
occupied states, electron spectra display<br />
pronounced shoul<strong>de</strong>rs at intermediate energies,<br />
which are not present when the surface is <strong>de</strong>scribed<br />
in a simpler way by employing a finite<br />
step potential to respresent the electron surfaceinteraction<br />
(Jellium mo<strong>de</strong>l). These shoul<strong>de</strong>rs are<br />
also observed for emission out of the scattering<br />
plane and their positions are gradually shifted to<br />
lower electron energies as the emission angle<br />
increases.<br />
10<br />
100 keV H + Be(0001)<br />
dP/dk (arb. units.)<br />
1<br />
0.1<br />
0.01<br />
Jellium<br />
BSB<br />
1E-3<br />
50 100 150 200<br />
Energy (eV)<br />
Figure 2. Total emission spectra for 100 keV protons<br />
impinging on a Be(0001) surface. BSB results<br />
are compared with Jellium mo<strong>de</strong>l results.<br />
Remarkably, surface state effects completely<br />
dissapear when we calculate the total<br />
emission probability as a function of the electron<br />
energy. These results are shown in Fig. 2.<br />
References<br />
[1] V.M. Silkin et al, J. Phys.: Con<strong>de</strong>ns. Matter<br />
20, 304209 (2008)<br />
[2] M. N. Faraggi et al, Phys. Rev. A 69,<br />
042901 (2004)<br />
[3] E. V. Chulkov, V. M. Silkin and P. M.<br />
Echenique, Surf. Sci. 391, L1217 (1997);<br />
437, 330 (1999)<br />
[4] M. N. Faraggi et al, Phys. Rev. A 72,<br />
012901 (2005).<br />
66 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Monte Carlo simulation for proton track structure in biological matter<br />
H. Lekadir 1 , C. Champion 1 , S. Incerti 2 , M. E. Galassi 3 , O. Fojón 3 , R. D. Rivarola 3 , and<br />
J. Hanssen 1<br />
1 Laboratoire <strong>de</strong> Physique Moléculaire et <strong>de</strong>s Collisions, Université Paul Verlaine-Metz, Metz, France<br />
2 Université Bor<strong>de</strong>aux 1, CNRS/IN2P3, CENBG, Bor<strong>de</strong>aux-Gradignan, France<br />
3 Instituto <strong>de</strong> <strong>Física</strong> Rosario, CONICET, <strong>Universidad</strong> Nacional <strong>de</strong> Rosario, Rosario, Argentina<br />
Corresponding author: lekadir@univ-metz.fr<br />
Monte Carlo simulations are well suited<br />
for <strong>de</strong>scribing the transport of charged particles<br />
in matter and more particularly in biological<br />
medium for predicting the radio-induced biological<br />
consequences.<br />
Ion beams are commonly used in radiotherapy<br />
essentially due to their physical and radiobiological<br />
characteristics which radically differ<br />
from those of conventional radiation beams<br />
(photons). Nowadays, protons are employed in<br />
many countries for treating particular pathologies.<br />
In<strong>de</strong>ed, in comparison to conventional<br />
techniques, protons offer an increased biological<br />
efficiency and a better ballistic by <strong>de</strong>positing in<br />
particular a large part of their initial energy in a<br />
narrow region - at the end of their path- called<br />
the Bragg peak region. Then, they allow a better<br />
protection of organs at risk in cancer therapy.<br />
To mo<strong>de</strong>l in <strong>de</strong>tails the track-structure of<br />
protons in biological matter, we have then <strong>de</strong>veloped<br />
a full-history Monte Carlo co<strong>de</strong> called<br />
TILDA2 which is able to <strong>de</strong>scribe, step by step,<br />
all the proton induced-collisions in biological<br />
matter, this latter being alternatively mo<strong>de</strong>lled<br />
by water and by some of its most important biological<br />
entities, namely, the DNA bases. The<br />
originality of our co<strong>de</strong> resi<strong>de</strong>s in the physical<br />
processes that are integrated. Thus, TILDA2<br />
takes into account a large panel of ionizing processes<br />
such as single and double ionization and<br />
capture, transfer ionization and excitation.<br />
To do that, we have first investigated different<br />
theoretical mo<strong>de</strong>ls for providing the<br />
nee<strong>de</strong>d input data, namely, the total cross sections:<br />
a first classical one based on a CTMC-<br />
COB [1,2] approach and two quantum mechanical<br />
ones, namely, a Coulomb Born (CB1) mo<strong>de</strong>l<br />
and a continuum-distorted wave eikonal-initialstate<br />
(CDW-EIS) one. All the obtained cross<br />
sections have been validated via theory/exp<br />
comparisons.<br />
TCS (10 -16 cm 2 )<br />
10 3 a) H 2<br />
O<br />
10 2<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
10 -3<br />
10 -4<br />
10 2 10 3 10 4<br />
7<br />
Inci<strong>de</strong>nt energy (keV/u)<br />
b) Guanine<br />
10 2 10 3 10 4<br />
Figure 1. Total cross sections of the ionizing<br />
processes inclu<strong>de</strong>d into the Monte Carlo co<strong>de</strong><br />
TILDA2 for <strong>de</strong>scribing the proton transport in water<br />
and guanine.<br />
Un<strong>de</strong>r these conditions, we have access to<br />
a large number of physical quantities such as<br />
stopping power, energy <strong>de</strong>position, charge fraction,<br />
range… in water and DNA components.<br />
Then, we have shown that the energy <strong>de</strong>posit<br />
patterns were extremely <strong>de</strong>pen<strong>de</strong>nt on the<br />
medium <strong>de</strong>scription.<br />
References<br />
[1] H. Lekadir et al., Nucl. Instr. Meth. Phys<br />
Res. B 267, 1014 (2009).<br />
[2] H. Lekadir et al., Phys. Rev. A 79, 062710<br />
(2009).<br />
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Multiple differential cross sections for the ionization from the 1B 1 orbital of liquid water molecule<br />
by fast electron impact<br />
M.L. <strong>de</strong> Sanctis 1 , O. Fojón 1 , C. Stia 1 , R. Vuilleumier 2 and M.-F. Politis 3<br />
1 Instituto <strong>de</strong> <strong>Física</strong> Rosario (CONICET-UNR), Pellegrini 250, (2000) Rosario, Argentina<br />
2 LPTMC, UMR-CNRS 7600, Université Pierre et Marie Curie 4 place Jussieu, 75005, Paris, France<br />
3 IMPMC, Université Pierre et Marie Curie, Campus Boucicaut, 140 rue <strong>de</strong> Lourmel, 75015, Paris, France<br />
email: ml<strong>de</strong>sanc@fceia.unr.edu.ar<br />
Ionization of water molecules in liquid<br />
phase is of relevance in several domains such as<br />
radiobiology and medical physics. As the<br />
biological matter is composed mainly of water,<br />
the analysis of this reaction is crucial to<br />
un<strong>de</strong>rstand the damage provoked to living tissue<br />
by the ionizing radiations. In particular, the<br />
production of low energy secondary electrons<br />
resulting from a primary ionization reaction of<br />
water is of importance to elucidate the<br />
mechanisms that lead to cell alteration.<br />
Therefore, we study the single ionization<br />
of water molecules in liquid phase by electron<br />
impact at high impact energies, i.e., hundreds of<br />
eV. We compute multiple differential cross<br />
sections (MDCS) by means of a simple first<br />
or<strong>de</strong>r mo<strong>de</strong>l. To represent the initial state of the<br />
molecule, we employ wavefunctions obtained<br />
through a Wannier orbital formalism that<br />
transforms the wavefunction of the whole liquid<br />
system into electronic orbitals localized over<br />
each water molecule in the liquid phase [1]. In<br />
particular, we consi<strong>de</strong>r coplanar geometries in<br />
which the inci<strong>de</strong>nt, scattered and ejected<br />
electrons lie in the same plane. Moreover, we<br />
analyze asymmetric kinematic conditions for the<br />
scattered and ejected electrons (ejected energies<br />
of some eV). By means of an approximate static<br />
potential, we obtain an estimation of the<br />
influence of the passive electrons of the<br />
molecule (those not ionized) on the ionization<br />
process. We compute MDCS for the 1B 1 orbital<br />
of the water molecule as a function of the<br />
ejection angle at <strong>de</strong>finite scattering angle,<br />
inci<strong>de</strong>nt and ejected energies, and for fixed<br />
orientations of the molecule. It is observed that<br />
MDCS <strong>de</strong>pend strongly on the orientation of the<br />
molecule. As experimental results of MDCS at<br />
fixed molecular orientations for liquid water are<br />
not available, we compare our theoretical<br />
predictions with other theoretical ones obtained<br />
for water molecules in gas phase [2]. In addition,<br />
as molecules are randomly oriented in<br />
experiments with water vapor [3], we also<br />
present MDCS averaged over all molecular<br />
orientations. The main physical features of the<br />
experiments (such as binary and recoil peaks)<br />
are similar to the ones observed in our results.<br />
Finally, we compare them with previous<br />
Fig 1. MDCS averaged over all molecular<br />
orientations. E i = 250 eV, E e = 10 eV and θ s<br />
=15º. Full line, present results for the liquid<br />
phase. Solid circles, experiments for the gas<br />
phase [3] conveniently normalized. Dashed line,<br />
previous caculations for the gas phase [4].<br />
Dotted line, FBA-CW for the liquid phase [6].<br />
Dash-dotted lines, FBA-CW for the gas phase<br />
[6].<br />
theoretical predictions by other authors for gas<br />
phase [4] in which the bound state of the water<br />
molecule is <strong>de</strong>scribed by means of single<br />
68 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
centered Moccia's orbitals [5]. It is worthy to<br />
mention that this is the only difference in the<br />
theoretical treatment of both mo<strong>de</strong>ls. Also, we<br />
compare with recent calculations for both<br />
thermodynamical phases here analysed, obtained<br />
again within a similar theoretical framework but<br />
now with monocentric wavefunctions for the<br />
water molecule constructed by employing a<br />
Gaussian basis [6].<br />
In Fig. 1, we present our theoretical<br />
MDCS averaged over all molecular orientations<br />
for an inci<strong>de</strong>nt energy E i = 250 eV, ejected<br />
energy E e = 10 eV and scattering angle θ s =15º.<br />
We have conveniently normalized the<br />
experiments for the gas phase as they were<br />
obtained in a relative scale [3]. As can be seen,<br />
our results <strong>de</strong>scribe the characteristic two-lobe<br />
structure found in the experimental data for the<br />
binary region. Moreover, all the theoretical<br />
predictions consi<strong>de</strong>red in the figure present<br />
binary and recoil structures in qualitative good<br />
agreement. In particular, our predictions present<br />
a very good agreement with the theoretical<br />
calculation for the liquid phase of Ref. [6].<br />
References<br />
[1] P. Hunt, M. Sprik and R. Vuilleumier, Chem.<br />
Phys. Lett. 376, 68 (2003).<br />
[2] C. Champion et al, Phys. Rev. A 63, 052720<br />
(2001); C. Champion et al, Phys. Rev. A 72,<br />
059906 (2005).<br />
[3] D. S. Milne et al, Phys. Rev. A 69, 032701<br />
(2004).<br />
[4] C. Champion et al, Phys. Rev. A 73, 012717<br />
(2006).<br />
[5] R. Moccia, J. Chem. Phys. 40 2186 (1964).<br />
[6] C. Champion, Phys. Med. Biol. 55, 11<br />
(2010).<br />
69 Valparaíso, Chile
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I<strong>de</strong>ntificação dos caminhos <strong>de</strong> fragmentação da molécula <strong>de</strong> CHClF 2 quando<br />
ionizada por elétrons<br />
L. Sigaud 1 , Natalia Ferreira 1 , V.L.B. <strong>de</strong> Jesus 2 , W. Wolff 1 , A.L.F. <strong>de</strong> Barros 3 , A.C.F.<br />
dos Santos 1 , R.S. Menezes 2 , A.B. Rocha 4 , M.B. Shah 5 , E.C. Montenegro 1<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, 21941-972, Rio <strong>de</strong> Janeiro, RJ, Brasil<br />
2 Instituto Fe<strong>de</strong>ral <strong>de</strong> Educação, Ciência e Tecnologia do Rio <strong>de</strong> Janeiro, 26530-060, Nilópolis, RJ, Brasil<br />
3 CEFET/RJ, 20271-110, Rio <strong>de</strong> Janeiro, RJ, Brasil<br />
4 Instituto <strong>de</strong> Química, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, 21941-614, Rio <strong>de</strong> Janeiro, RJ, Brasil<br />
5 School of Maths & Physics, The Queen´s University of Belfast, Belfast, UK<br />
email address corresponding author: lucas@if.ufrj.br<br />
O impacto negativo ao meio-ambiente<br />
causado pelo aumento do buraco da camada<br />
<strong>de</strong> ozônio é bem conhecido. Em 1974, Molina<br />
e Rowland <strong>de</strong>scobriram que a maior parte dos<br />
compostos CFC utilizados na indústria <strong>de</strong>s<strong>de</strong><br />
a década <strong>de</strong> 30 ainda estavam presentes em<br />
camadas altas da atmosfera [1]. Na baixa<br />
estratosfera, moléculas <strong>de</strong> CFC po<strong>de</strong>m ser<br />
fragmentadas, liberando um átomo <strong>de</strong> cloro,<br />
que, juntamente com o bromo, são os<br />
principais responsáveis pela <strong>de</strong>pleção da<br />
camada <strong>de</strong> ozônio.<br />
Originalmente acreditava-se que o<br />
mecanismo responsável pela fragmentação<br />
das moléculas <strong>de</strong> CFC fossem fótons<br />
energéticos provenientes do Sol, mas estudos<br />
recentes mostram que elétrons <strong>de</strong> chuveiros<br />
gerados por raios cósmicos po<strong>de</strong>m ser<br />
candidatos viáveis para a produção <strong>de</strong> átomos<br />
<strong>de</strong> cloro na estratosfera [2,3]. Por isso, um<br />
estudo da fragmentação <strong>de</strong> moléculas <strong>de</strong> CFC<br />
e HCFC (compostos CFC hidrogenados, a<br />
fim <strong>de</strong> diminuir seu impacto para a camada<br />
<strong>de</strong> ozônio) quando impactadas por elétrons é<br />
necessário, uma vez que alguns <strong>de</strong>sses<br />
compostos continuam sendo utilizados<br />
largamente na indústria, como é o caso do<br />
CHClF 2 .<br />
Para tanto, um canhão <strong>de</strong> elétrons<br />
operante na faixa <strong>de</strong> 40-450eV acoplado a<br />
uma célula gasosa com medição <strong>de</strong> pressão<br />
absoluta e um espectrômetro <strong>de</strong> massa por<br />
tempo <strong>de</strong> vôo montado na Universida<strong>de</strong><br />
Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro foi utilizado. As<br />
seções <strong>de</strong> choque <strong>de</strong> fragmentação da<br />
molécula <strong>de</strong> CHClF 2 quando impactada por<br />
elétrons foram medidas, fornecendo um<br />
indicador preciso para a produção <strong>de</strong> átomos<br />
<strong>de</strong> cloro.<br />
As seções <strong>de</strong> choque absolutas e<br />
parciais para cada um dos principais canais<br />
<strong>de</strong> fragmentação (a saber, H + , C + , CH + , F + ,<br />
CF + , CHF + , Cl + , (CF + 2 + CHF + 2 ), (CClF + +<br />
CHClF + +<br />
2 ) e (CClF 2 + CHClF + 2 )) foram<br />
obtidas, e os resultados comparados com<br />
previsões teóricas calculadas a partir <strong>de</strong> um<br />
mo<strong>de</strong>lo simples baseado na aproximação <strong>de</strong><br />
Born e funções <strong>de</strong> onda hidrogenói<strong>de</strong>s [4].<br />
A partir <strong>de</strong>ssa comparação, as razões <strong>de</strong><br />
fragmentação (branching ratios) pu<strong>de</strong>ram ser<br />
obtidas empiricamente, ajustando-se os<br />
parâmetros livres às seções <strong>de</strong> choque<br />
calculadas e aos dados obtidos<br />
experimentalmente.<br />
Os resultados obtidos [5] indicam que a<br />
molécula <strong>de</strong> CHClF 2 é altamente instável ao<br />
ser ionizada por elétrons nesta faixa <strong>de</strong><br />
energia - isto é, quando um <strong>de</strong> seus elétrons é<br />
removido, a maior probabilida<strong>de</strong> é a da<br />
molécula-mãe se fragmentar, pois a seção <strong>de</strong><br />
choque <strong>de</strong> produção do íon CHClF + 2 é uma<br />
das menores observadas. A maior <strong>de</strong> todas é<br />
justamente a do canal <strong>de</strong> fragmentação<br />
responsável pela emissão do átomo <strong>de</strong> cloro<br />
(CF +<br />
2 ou CHF + 2 + Cl 0 ), conforme ilustra a<br />
Figura 1.<br />
Além disso, o estudo realizado dos<br />
caminhos possíveis <strong>de</strong> fragmentação da<br />
70 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
molécula <strong>de</strong> CHClF 2 indicam que não apenas<br />
vacâncias nos orbitais do átomo <strong>de</strong> cloro<br />
po<strong>de</strong>m gerar sua emissão, mas também que<br />
elétrons retirados dos orbitais do átomo <strong>de</strong><br />
flúor contribuem significativamente para a<br />
emissão do átomo <strong>de</strong> cloro. Esse aspecto<br />
interessante aponta para uma fragmentação<br />
em um sítio diferente do local on<strong>de</strong> a<br />
ionização <strong>de</strong> fato ocorreu, por meio <strong>de</strong> um<br />
rearranjo local dos orbitais eletrônicos do<br />
átomo <strong>de</strong> flúor, que po<strong>de</strong> gerar rearranjos<br />
eletrônicos e excitações vibracionais na<br />
molécula.<br />
Figura 1. Espectro típico obtido na<br />
fragmentação da molécula <strong>de</strong> CHClF 2<br />
(representada nos <strong>de</strong>talhes) por impacto <strong>de</strong><br />
elétrons. Po<strong>de</strong>-se notar claramente a<br />
predominância do canal responsável pela<br />
emissão do átomo <strong>de</strong> cloro (CF 2 + + CHF 2 + ), bem<br />
como o baixa probabilida<strong>de</strong> do canal que<br />
representa a ionização simples da molécula-mãe.<br />
Os cálculos teóricos, mesmo baseados<br />
em um mo<strong>de</strong>lo simples, fornecem, portanto,<br />
uma <strong>de</strong>scrição razoavelmente <strong>de</strong>talhada dos<br />
caminhos mais prováveis para a<br />
fragmentação da molécula por elétrons. Em<br />
particular, essa comparação mostra um<br />
gran<strong>de</strong> indício <strong>de</strong> não-localida<strong>de</strong> entre a<br />
ionização e o processo <strong>de</strong> fragmentação, a<br />
qual contribui significantemente para a<br />
instabilida<strong>de</strong> do CHClF 2 [5].<br />
References<br />
[1] F.S. Rowland and M.J. Molina, Nature 249,<br />
810 (1974).<br />
[2] Q.-B. Lu and L. Sanche, Phys. Rev. Lett. 87,<br />
078501 (2001).<br />
[3] J.A.M. Pereira, Nucl. Instr. Meth. B 240, 133<br />
(2005).<br />
[4] E.C. Montenegro, A.C.F. dos Santos e G.M.<br />
Sigaud, Application of Accelerators in Research<br />
and Industry 2000 (AIP Conf. Proc. 576) ed. J.L.<br />
Duggan and I.L. Morgan (New York: AIP<br />
Press), 96 (2001).<br />
[5] L. Sigaud, Natalia Ferreira, V.L.B. <strong>de</strong><br />
Jesus, W. Wolff, A.L.F. <strong>de</strong> Barros,<br />
A.C.F. dos Santos, R.S. Menezes,<br />
A.B. Rocha, M.B. Shah and E.C.<br />
Montenegro, J. Phys. B: At. Mol. Opt. Phys.<br />
43, 105203 (2010).<br />
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Café Brasileiro: Estudo da Concentração Elementar Utilizando Feixes Iônicos<br />
Rafaela Debastiani 1 , Carla Eliete Iochims dos Santos 1 , Liana Appel Boufleur 1 , Masahiro Hatori 1 , Débora Elisa<br />
Peretti 1 , Vanessa Sobrosa Souza 1 , Mateus Maciel Ramos 1 , Elis Moura Stori 1 , Cláudia Telles <strong>de</strong> Souza 1 , Livio<br />
Amaral 1 , Johnny Ferraz Dias 1<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio Gran<strong>de</strong> do Sul, Av. Bento Gonçalves 9500, Porto Alegre, Brasil<br />
Email autor correspon<strong>de</strong>nte: rafa_<strong>de</strong>bas@yahoo.com.br<br />
Sendo o café um produto alimentício<br />
nutracêutico (nutricional e farmacêutico) [1]<br />
amplamente consumido, é importante termos o<br />
conhecimento sobre sua composição química, mais<br />
especificamente, sua composição elementar. Alguns<br />
<strong>de</strong>sses elementos po<strong>de</strong>m ser metais com potencial<br />
bio-cumulativo, que ingeridos em <strong>de</strong>terminadas<br />
doses, po<strong>de</strong>m causar intoxicação. Em vista disso,<br />
utilizando a técnica PIXE (Particle-Induced X-ray<br />
Emission) e complementarmente a técnica RBS<br />
(Rutherford Backscattering Spectrometry) foi<br />
realizada a análise elementar do café brasileiro.<br />
PIXE é uma técnica baseada na emissão <strong>de</strong> raios X<br />
característicos <strong>de</strong> cada elemento da amostra, quando<br />
esta é irradiada por prótons <strong>de</strong> alta energia<br />
(aproximadamente 2 MeV) provenientes <strong>de</strong> um<br />
acelerador <strong>de</strong> partículas. Esta técnica possui alta<br />
sensibilida<strong>de</strong> (da or<strong>de</strong>m <strong>de</strong> ppm), é não <strong>de</strong>strutiva e<br />
<strong>de</strong>termina simultaneamente elementos a partir do<br />
sódio. A técnica RBS foi utilizada para <strong>de</strong>terminação<br />
da matriz (composição orgânica – carbono,<br />
oxigênio) da amostra. Para utilização <strong>de</strong> ambas as<br />
técnicas, é necessário que as amostras estejam<br />
sólidas e homogêneas. Para tanto, inicialmente<br />
analisamos pó <strong>de</strong> oito marcas <strong>de</strong> café, cujos<br />
elementos encontrados foram Mg, Al, P, S, Cl, K,<br />
Ca, Ti, Mn, Fe, Cu, Zn, Br, Rb e Sr. O resultado<br />
qualitativo da média <strong>de</strong> 18 amostras para cada uma<br />
das oito marcas <strong>de</strong> café po<strong>de</strong> ser observado na figura<br />
1. Em continuação, será selecionada uma marca com<br />
a qual será realizada a análise do processo <strong>de</strong><br />
preparação e ingestão da bebida (café em pó, café<br />
pelo qual a água passou e café líquido, propriamente<br />
dito).<br />
Figura 1. Espectro PIXE com a média <strong>de</strong> 18 amostras<br />
para cada uma das 8 marcas <strong>de</strong> café.<br />
Referências[1]<br />
http://www.abic.com.br/prog_merenda.html<br />
72 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Coherencia y localización parcial en emisión electrónica simple <strong>de</strong><br />
moléculas diatómicas<br />
C. Tachino 1 , M. Galassi 1 , F. Martín 2 , y R. Rivarola 1<br />
1<br />
Instituto <strong>de</strong> <strong>Física</strong> Rosario, CONICET – <strong>Universidad</strong> Nacional <strong>de</strong> Rosario, Av. Pellegrini 250, 2000 Rosario,<br />
Argentina<br />
2<br />
<strong>Departamento</strong> <strong>de</strong> Química, Módulo 13, <strong>Universidad</strong> Autónoma <strong>de</strong> Madrid, 28049, Madrid, España<br />
email address corresponding author: rivarola@fceia.unr.edu.ar<br />
La emisión coherente <strong>de</strong> electrones<br />
<strong>de</strong>s<strong>de</strong> las cercanías <strong>de</strong> los núcleos <strong>de</strong> una<br />
molécula diatómica da lugar a los <strong>de</strong>nominados<br />
efectos <strong>de</strong> interferencia, siendo la naturaleza<br />
ondulatoria <strong>de</strong> estas partículas el origen<br />
<strong>de</strong> dicho fenómeno. Los primeros indicios<br />
<strong>de</strong> la existencia <strong>de</strong> los característicos<br />
patrones oscilatorios en los espectros<br />
electrónicos fueron observados ya en la<br />
década <strong>de</strong> 1960 por Samson y Cairns [1]<br />
al estudiar el proceso <strong>de</strong> fotoionización <strong>de</strong><br />
electrones <strong>de</strong> valencia <strong>de</strong> moléculas N 2 y<br />
O 2 . Tiempo más tar<strong>de</strong>, Cohen y Fano [2]<br />
pudieron establecer una relación entre<br />
este hecho y la emisión coherente <strong>de</strong> electrones<br />
<strong>de</strong>s<strong>de</strong> las proximida<strong>de</strong>s <strong>de</strong> los núcleos<br />
moleculares analizando <strong>de</strong> manera<br />
teórica el problema <strong>de</strong> fotoionización <strong>de</strong>l<br />
ion H 2+ . Sin embargo, las primeras evi<strong>de</strong>ncias<br />
experimentales <strong>de</strong> la existencia <strong>de</strong><br />
este fenómeno fueron obtenidas recién en<br />
el año 2001, cuando Stolterfoth y colaboradores<br />
[3] pudieron observar patrones <strong>de</strong><br />
interferencia en las secciones eficaces <strong>de</strong><br />
ionización para el sistema Kr 34+ (60<br />
MeV/u) + H 2 . Des<strong>de</strong> entonces, los estudios<br />
sobre efectos <strong>de</strong> interferencia se han<br />
ampliado, lográndose no sólo una mayor<br />
cantidad <strong>de</strong> evi<strong>de</strong>ncias experimentales<br />
sino también mo<strong>de</strong>los teóricos cada vez<br />
más sofisticados que nos permiten enten<strong>de</strong>r<br />
en mayor medida la esencia <strong>de</strong> este<br />
tipo <strong>de</strong> procesos.<br />
Es nuestra intención exponer en esta<br />
oportunidad los resultados obtenidos en<br />
un trabajo previo [4] con el fin <strong>de</strong> analizar<br />
la existencia <strong>de</strong> interferencias en los patrones<br />
<strong>de</strong> ionización simple <strong>de</strong> iones moleculares<br />
HeH + y <strong>de</strong> moléculas diatómicas<br />
que posean más <strong>de</strong> un orbital molecular<br />
en su estado fundamental. Para realizar<br />
este trabajo, utilizamos el mo<strong>de</strong>lo CDW-<br />
EIS junto con una aproximación <strong>de</strong> dos<br />
centros efectivos (TEC) para <strong>de</strong>scribir la<br />
dinámica <strong>de</strong> la colisión. En cuanto a los<br />
núcleos <strong>de</strong>l blanco, se ha asumido que las<br />
posiciones <strong>de</strong> los mismos permanecen fijas<br />
durante la reacción. Los orbitales moleculares<br />
fueron representados mediante<br />
una combinación lineal <strong>de</strong> orbitales <strong>de</strong><br />
tipo Slater centrados en cada núcleo.<br />
En lo que respecta al blanco heteronuclear<br />
HeH + , se muestra que las interferencias<br />
son visibles aún <strong>de</strong>spués <strong>de</strong> promediar<br />
las distribuciones electrónicas angulares<br />
sobre todas las posibles orientaciones<br />
moleculares [5]. De la comparación<br />
entre estos espectros y los calculados<br />
para moléculas H 2 , se observa que las oscilaciones<br />
en el caso heteronuclear son<br />
menos pronunciadas que aquellas correspondientes<br />
al caso homonuclear. Este<br />
comportamiento se atribuye a la localización<br />
parcial <strong>de</strong> electrones alre<strong>de</strong>dor <strong>de</strong> la<br />
partícula alfa en el blanco HeH + .<br />
Para moléculas multielectrónicas tales<br />
como N 2 , O 2 y CO, se muestran los espectros<br />
correspondientes a secciones eficaces<br />
diferenciales en energía y orientación<br />
<strong>de</strong>l electrón emitido, y en orientación<br />
<strong>de</strong>l blanco molecular. En estos cálculos se<br />
consi<strong>de</strong>ra una geometría coplanar en la<br />
que el electrón emitido, el proyectil y la<br />
molécula se encuentran todos en el mismo<br />
plano, y se analizan dos orientaciones mo-<br />
73 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
leculares <strong>de</strong>finidas- paralela y perpendicular<br />
a la dirección <strong>de</strong> inci<strong>de</strong>ncia <strong>de</strong>l proyectil.<br />
También se muestras secciones eficaces<br />
doble diferenciales, las cuales se<br />
obtienen promediando las distribuciones<br />
electrónicas angulares sobre todas las posibles<br />
orientaciones <strong>de</strong> la molécula.<br />
Referencias<br />
[1] J. Samson y R. Cairns, J. Opt. Soc. Am.<br />
55, 1035 (1965).<br />
[2] H. Cohen y U. Fano, Phys. Rev. 150, 30<br />
(1966).<br />
[3] N. Stolterfoht et al, Phys. Rev. Lett. 87,<br />
023201 (2001).<br />
[4] C. Tachino et al., J. Phys. B 42, 075203<br />
(2009).<br />
[5] C. Tachino et al., J. Phys. B 43, 135203<br />
(2010).<br />
Figura 1. Comparación entre los cocientes <strong>de</strong> secciones<br />
eficaces doble diferenciales (DDCS) para el<br />
ion molecular HeH + (línea sólida) y para la molécula<br />
<strong>de</strong> hidrógeno (línea <strong>de</strong> trazos) para diferentes energías<br />
<strong>de</strong> impacto <strong>de</strong> protones y diferentes ángulos <strong>de</strong><br />
emisión <strong>de</strong>l electrón..<br />
Figura 2. Cocientes <strong>de</strong> secciones eficaces doble<br />
diferenciales por orbital molecular para el sistema<br />
H + (1 MeV) + N 2, para un ángulo <strong>de</strong><br />
emisión <strong>de</strong>l electrón igual a 30º.<br />
74 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Estados selectivos <strong>de</strong> captura <strong>de</strong> electrones en colisiones <strong>de</strong> 3 He 2+ +He a<br />
energías intermedias <strong>de</strong> impacto aplicando la técnica COLTRIMS<br />
M. Alessi 1 , S. Otranto 2 , D. Fregenal 1 , P. Focke 1<br />
1 Centro Atómico Bariloche, S. C. <strong>de</strong> Bariloche, 8400, Río Negro, Argentina<br />
2 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong> <strong>Universidad</strong> Nacional <strong>de</strong>l Sur, 8000 Bahía Blanca, Buenos Aires Argentina.<br />
email <strong>de</strong>l autor correspondiente: alessi@cab.cnea.gov.ar<br />
Durante la última década el <strong>de</strong>sarrollo <strong>de</strong><br />
la técnica COLTRIMS (Cold Target Recoil - Ion<br />
Momentum Spectroscopy) ha provocado un<br />
cambio fundamental en la investigación <strong>de</strong> colisiones<br />
atómicas y moleculares. Dicha técnica<br />
también conocida como Reaction Microscope,<br />
es actualmente una <strong>de</strong> las herramientas más<br />
completas que permite reconstruir con alta resolución<br />
y en forma <strong>de</strong>tallada procesos <strong>de</strong> colisiones<br />
que involucren átomos, moléculas y clusters<br />
en estado gaseoso.<br />
Lo novedoso <strong>de</strong> dicha técnica es la incorporación<br />
e integración <strong>de</strong> blancos fríos supersónicos,<br />
<strong>de</strong>tectores bidimensionales <strong>de</strong> partículas y<br />
espectrómetros electrostáticos; que junto con el<br />
<strong>de</strong>sarrollo <strong>de</strong> electrónica ultra-rapida y la técnica<br />
<strong>de</strong> medición por tiempo <strong>de</strong> vuelo (TOF), la convierten<br />
en una herramienta fundamental para el<br />
estudio <strong>de</strong> procesos que involucren transferencia<br />
<strong>de</strong> carga, simple y múltiple ionización por iones,<br />
electrones y fotones, entre otros procesos.<br />
La utilización <strong>de</strong> un haz supersónico colimado<br />
para la producción <strong>de</strong> blancos fríos localizados<br />
y <strong>de</strong> <strong>de</strong>tectores <strong>de</strong> partículas sensibles a<br />
la posición, es lo que <strong>de</strong>termina la resolución y<br />
precisión en la medición <strong>de</strong> los momentos transferidos<br />
durante las colisiones.<br />
Dicha técnica lleva poco más <strong>de</strong> diez años<br />
<strong>de</strong> <strong>de</strong>sarrollo y aplicación, y se encuentra en<br />
plena producción en su país gestador, Alemania<br />
y en países como Estados Unidos, Francia y Japón.<br />
Luego <strong>de</strong> varios años <strong>de</strong> <strong>de</strong>sarrollo se logró<br />
la optimización <strong>de</strong> diversas partes <strong>de</strong> los diseños<br />
originales. En nuestro país, es una técnica nueva<br />
y se ha incorporado en los últimos años en nuestro<br />
laboratorio. La versión <strong>de</strong>l equipamiento implementado<br />
en el Centro Atómico Bariloche correspon<strong>de</strong><br />
a uno <strong>de</strong> las primeras variantes <strong>de</strong> la<br />
técnica <strong>de</strong>sarrollada en Alemania, con algunas<br />
modificaciones que fueron incorporándose durante<br />
el montaje y caracterización <strong>de</strong>l presente<br />
equipo.<br />
La línea experimental <strong>de</strong> Bariloche consta<br />
<strong>de</strong> un sistema <strong>de</strong> transporte y colimación <strong>de</strong>l haz<br />
<strong>de</strong> proyectiles (iones/átomos) provenientes <strong>de</strong>l<br />
acelerador Kevatron tipo Cockcroft-Walton, que<br />
permite alcanzar energías <strong>de</strong>l or<strong>de</strong>n <strong>de</strong> 10 a<br />
250 keV. Dicho haz es transportado hacia la<br />
zona <strong>de</strong> colisión, <strong>de</strong>ntro <strong>de</strong> una cámara que alcanza<br />
presiones <strong>de</strong> base <strong>de</strong>l or<strong>de</strong>n <strong>de</strong> 10 -8 Torr,<br />
don<strong>de</strong> impacta con un haz supersónico gaseoso<br />
enfriado, ya sea atómico o molecular. En nuestro<br />
caso, el enfriamiento <strong>de</strong>l blanco se produce durante<br />
una expansión adiabática <strong>de</strong>l mismo, a través<br />
<strong>de</strong> un sistema <strong>de</strong> tobera-skimmer. Tal enfriamiento<br />
tiene el objetivo <strong>de</strong> reducir consi<strong>de</strong>rablemente<br />
la distribución <strong>de</strong> momentos inicial<br />
<strong>de</strong>l blanco, hasta llegar a ser <strong>de</strong>spreciable, comparada<br />
con los momentos transferidos durante<br />
los procesos <strong>de</strong> colisiones.<br />
Los fragmentos e iones en retroceso producidos<br />
durante las colisiones, son extraídos<br />
utilizando un espectrómetro electrostático y son<br />
<strong>de</strong>tectados por medio <strong>de</strong> un <strong>de</strong>tector sensible a la<br />
posición (DLD40) tipo multi-hit, conformado<br />
por micro-channelplates (MCP) y ánodo por<br />
líneas <strong>de</strong> retraso. Dicho <strong>de</strong>tector junto con la<br />
técnica <strong>de</strong> medición TOF, la incorporación <strong>de</strong><br />
campos eléctricos en la línea emergente <strong>de</strong>l proyectil<br />
y la utilización <strong>de</strong> <strong>de</strong>tectores ultra-rápidos<br />
(tipo channeltron) permiten medir en coinci<strong>de</strong>ncia<br />
los momentos <strong>de</strong> los iones producidos en las<br />
colisiones y el estado <strong>de</strong> carga <strong>de</strong>l proyectil<br />
emergente. Esta configuración <strong>de</strong> medición abre<br />
75 Valparaíso, Chile
Counts<br />
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
las puertas hacia una nueva técnica en la cual<br />
toda la cinemática producida durante la colisión<br />
pue<strong>de</strong> ser reconstruida, a través <strong>de</strong> la <strong>de</strong>terminación<br />
<strong>de</strong> la posición <strong>de</strong> impacto <strong>de</strong> los fragmentos<br />
residuales sobre <strong>de</strong>tectores bidimensionales<br />
y el tiempo <strong>de</strong> vuelo <strong>de</strong> los fragmentos y el proyectil.<br />
En este trabajo como muestra <strong>de</strong>l <strong>de</strong>sempeño<br />
y caracterización <strong>de</strong>l equipo, presentamos<br />
mediciones <strong>de</strong> captura simple <strong>de</strong> electrones en<br />
colisiones <strong>de</strong> 3 He 2+ como proyectil inci<strong>de</strong>nte<br />
sobre blancos <strong>de</strong> He. El estudio fue realizado<br />
en el rango <strong>de</strong> energías intermedias <strong>de</strong> 13.3 -<br />
100 keV/amu, rango en energías hasta ahora<br />
no explorado en la literatura. Fueron <strong>de</strong>terminadas<br />
las distribuciones <strong>de</strong> momentos longitudinales<br />
en las cuales se i<strong>de</strong>ntificaron las<br />
contribuciones <strong>de</strong> los distintos procesos <strong>de</strong><br />
captura asociados al estado fundamental y<br />
estados excitados (Fig. 1). Se <strong>de</strong>terminaron<br />
secciones eficaces <strong>de</strong> estados selectivos <strong>de</strong><br />
captura simple como función <strong>de</strong> la energía <strong>de</strong><br />
impacto <strong>de</strong>l proyectil. Los resultados obtenidos<br />
muestran un buen acuerdo con mediciones<br />
existentes <strong>de</strong>l grupo <strong>de</strong> Frankfurt [1],<br />
don<strong>de</strong> se exponen datos en el rango <strong>de</strong> energias<br />
<strong>de</strong> impacto <strong>de</strong> 60 keV/amu a 250<br />
keV/amu; así como con datos más resientes<br />
<strong>de</strong>l grupo <strong>de</strong> Lanzhou [2] a 7.5 keV/amu. Los<br />
datos experimentales presentados también<br />
son contrastados con resultados obtenidos en<br />
este trabajo con el método <strong>de</strong> trayectorias<br />
clasicas <strong>de</strong> Monte Carlo (Fig. 2).<br />
En este trabajo también por medio <strong>de</strong>l<br />
mo<strong>de</strong>lo dCTMC se ponen en evi<strong>de</strong>ncia las<br />
contribuciones <strong>de</strong> cada uno <strong>de</strong> los canales<br />
(1,1), (1,2), (2,1) y (3,1) en forma discriminada,<br />
muchos <strong>de</strong> los cuales no pue<strong>de</strong>n ser<br />
resueltos experimentalmente, como por<br />
ejemplo los canales (1,2) y (2,1), dada la simetría<br />
<strong>de</strong>l presente proceso.<br />
Cross section (cm 2 )<br />
8000<br />
6000<br />
4000<br />
2000<br />
Figura 1. Distribución <strong>de</strong> momentos longitudinales<br />
p x , <strong>de</strong> iones en retroceso <strong>de</strong> He + provenientes <strong>de</strong>l<br />
proceso <strong>de</strong> captura simple a 60 keV.<br />
10 -15 (n,n')=(1,1)<br />
a)<br />
(1,2)&(2,1)<br />
(1,>3)&(>3,1)<br />
10 -16<br />
(>2,>2)<br />
10 -17<br />
10 -18<br />
20 keV/amu<br />
(n,n´)=(1,1)<br />
0.75<br />
FWHM<br />
0<br />
-4 -3 -2 -1 0 1 2 3<br />
p x<br />
(a.u.)<br />
Figura 2. Secciones eficaces <strong>de</strong> captura para diferentes<br />
estados excitados. Símbolos llenos: este trabajo;<br />
símbolos abiertos: Mergel et al. [1] (Frankfurt<br />
group); símbolos abiertos divididos: Zhu et al. [2]<br />
(Lanzhou group); líneas: cálculo dCTMC presente.<br />
Lineas: cálculo dCTMC: línea sólida (1,1); línea <strong>de</strong><br />
trazos (1,2)&(2,1); puntos-trazos (1,≥3)&(≥3,1);<br />
línea <strong>de</strong> puntos (≥2, ≥2).<br />
Referencias<br />
(1,2) & (2,1)<br />
100<br />
10 100<br />
Energy (keV/amu)<br />
(> 2, > 2)<br />
1 2 3<br />
(1, > 3) & ( > 3,1)<br />
[1] V. Mergel, et al., Phys. Rev. Lett. 74, 2200,<br />
(1995).<br />
[2] X. L. Zhu, et al., Chi. Phys. Lett. 23, 587,<br />
(2006).<br />
10<br />
76 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Estudio <strong>de</strong> colisiones con proyectiles neutros y cargados sobre blancos<br />
moleculares <strong>de</strong> H 2 a energías intermedias <strong>de</strong> impacto con la técnica<br />
COLTRIMS<br />
M. Alessi, D. Fregenal, P. Focke<br />
Centro Atómico Bariloche, S. C. <strong>de</strong> Bariloche, 8400, Río Negro, Argentina.<br />
email <strong>de</strong>l autor correspondiente: alessi@cab.cnea.gov.ar<br />
La técnica COLTRIMS (Cold Target Recoil<br />
- Ion Momentum Spectroscopy) incorporada<br />
en los últimos años en el Centro Atómico Bariloche,<br />
es actualmente una <strong>de</strong> las herramientas<br />
más nuevas con la que cuenta la División Colisiones<br />
Atómicas para realizar estudios completos<br />
sobre la cinemática <strong>de</strong> colisiones <strong>de</strong> proyectiles<br />
neutros y cargados sobre blancos supersónicos<br />
enfriados. Dicha técnica, implementada y<br />
caracterizada en los últimos años, permite en su<br />
actual <strong>de</strong>sarrollo realizar mediciones <strong>de</strong> colisiones<br />
<strong>de</strong> haces livianos sobre blancos moleculares<br />
en estado gaseoso y estudiar procesos <strong>de</strong> transferencia<br />
<strong>de</strong> carga, excitación e ionización, tanto<br />
<strong>de</strong>l blanco como <strong>de</strong>l proyectil que involucren un<br />
cambio <strong>de</strong> carga <strong>de</strong>l proyectil.<br />
Varios estudios ya se encuentran en la literatura<br />
<strong>de</strong> procesos <strong>de</strong> colisiones <strong>de</strong> proyectiles<br />
cargados sobre blancos moleculares tanto <strong>de</strong><br />
COLTRIMS [1] como empleando otras técnicas<br />
[2], pero pocas referencias pue<strong>de</strong>n hallarse sobre<br />
proyectiles neutros interactuando con moléculas<br />
[3]. Este es un campo hasta el presente prácticamente<br />
no abordado y su comprensión aporta<br />
conocimientos en áreas vinculadas con procesos<br />
en la atmósfera, plasmas, física espacial y física<br />
médica, [4, 5, 6].<br />
En este trabajo se presentan mediciones<br />
<strong>de</strong> proyectiles atómicos neutros y cargados como<br />
He o , He + y H o , inci<strong>de</strong>ntes sobre el blanco<br />
molecular <strong>de</strong> H 2 , a energías <strong>de</strong> impacto intermedias<br />
<strong>de</strong> 6.25 y 50 keV/amu. La configuración<br />
básica <strong>de</strong> los procesos estudiados está dada en la<br />
Fig. 1, don<strong>de</strong> pue<strong>de</strong>n observarse, la dirección x,<br />
o longitudinal, don<strong>de</strong> inci<strong>de</strong> el proyectil y las<br />
dos direcciones transversales y y z, don<strong>de</strong> y es<br />
la dirección <strong>de</strong>l haz blanco, y z la dirección <strong>de</strong>l<br />
campo eléctrico <strong>de</strong> extracción <strong>de</strong> los fragmentos,<br />
en el espectrómetro <strong>de</strong>l sistema COLTRIMS.<br />
Figura 1. Esquema simplificado <strong>de</strong> procesos estudiados<br />
con la técnica COLTRIMS. Don<strong>de</strong> x es la direccion<br />
<strong>de</strong>l proyectil, y es la dirección <strong>de</strong>l haz supersónico<br />
(jet), z es la dirección <strong>de</strong>l campo <strong>de</strong> extracción.<br />
b y v p son el parámetro <strong>de</strong> impacto y la velocidad<br />
<strong>de</strong>l proyectil inci<strong>de</strong>nte. es el ángulo <strong>de</strong>l eje<br />
intermolecular con la dirección <strong>de</strong> inci<strong>de</strong>ncia <strong>de</strong>l<br />
proyectil, y es el ángulo azimutal en el plano y-z.<br />
En particular en este caso, para proyectiles<br />
cargados, se presentan mediciones <strong>de</strong> procesos<br />
<strong>de</strong> captura simple <strong>de</strong>l proyectil y excitación<br />
<strong>de</strong>l blanco para el sistema <strong>de</strong> colisión He + + H 2<br />
y para el caso <strong>de</strong> proyectiles neutros, se analizan<br />
procesos <strong>de</strong> pérdida, ionización y excitación.<br />
En todos los procesos se centra la atención en la<br />
emisión <strong>de</strong> fragmentos <strong>de</strong> H 2 + en todo su rango<br />
<strong>de</strong> energías, como así también en la emisión<br />
<strong>de</strong> H + pero solo para rangos <strong>de</strong> energías <strong>de</strong><br />
emisión menores a 4 eV, es <strong>de</strong>cir, el estudio<br />
se enfoca en la emisión <strong>de</strong> protones lentos.<br />
Como análisis <strong>de</strong> la cinemática se presentan<br />
las distribuciones <strong>de</strong> transferencias <strong>de</strong><br />
momentos longitudinales (P x ) y transversales<br />
(P y - P z ) <strong>de</strong> los recoils <strong>de</strong> H 2 + (Fig.2) y H + , se<br />
77 Valparaíso, Chile
Py (a.u.)<br />
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
estudia su emisión angular y simetrías<br />
(Fig.3), como así también <strong>de</strong>flexión <strong>de</strong>l proyectil,<br />
por ejemplo para el caso <strong>de</strong> captura<br />
simple. Los fragmentos <strong>de</strong> H + <strong>de</strong> baja energía<br />
están vinculados con la disociación <strong>de</strong>l estado<br />
fundamental <strong>de</strong>l ion H 2 + (GSD).<br />
Para el caso <strong>de</strong> proyectiles neutros en<br />
particular, se comienzan a dar muestras <strong>de</strong> la<br />
transferencia <strong>de</strong> momentos a distintas energías<br />
y análisis <strong>de</strong> procesos con proyectiles<br />
con uno y dos electrones.<br />
Figura 2. Distribución <strong>de</strong> momentos longitudinal P x<br />
y una <strong>de</strong> las componentes transversales P y (dirección<br />
<strong>de</strong>l jet) para el proceso <strong>de</strong> captura simple <strong>de</strong><br />
He + + H 2 a 25 keV.<br />
25<br />
20<br />
15<br />
10<br />
5<br />
0<br />
-5<br />
-10<br />
-15<br />
-20<br />
-25<br />
-30<br />
-30 -25 -20 -15 -10 -5 0 5 10 15 20 25<br />
Px (a.u)<br />
100<br />
10<br />
1<br />
1<br />
10<br />
100<br />
180<br />
9000<br />
8500<br />
8000<br />
7500<br />
7000<br />
6500<br />
6000<br />
5500<br />
5000<br />
4500<br />
4000<br />
3500<br />
3000<br />
2500<br />
2000<br />
1500<br />
1000<br />
500<br />
0<br />
150<br />
210<br />
120<br />
240<br />
(grados)<br />
90<br />
270<br />
Figura 3. Emisión angular <strong>de</strong> los fragmentos <strong>de</strong> H +<br />
en la disociación <strong>de</strong>l estado fundamental GSD<br />
H 2<br />
+<br />
(1s g<br />
) → H + + H o (1s) para el sistema<br />
He + + H 2 →He o + H + + H (captura y excitación).<br />
Círculos llenos 200 keV, círculos abiertos 25 keV.<br />
Referencias<br />
60<br />
300<br />
30<br />
330<br />
0<br />
100<br />
10<br />
1<br />
1<br />
10<br />
100<br />
180<br />
(grados)<br />
[1] M. A. Abdallah, et al., Phys. Rev. A, 62,<br />
012711, (2000).<br />
[2] V. V. Afrosimov, et al., Sov. Phys. JETP, 29,<br />
4, (1969).<br />
[3] E. Horsdal Pe<strong>de</strong>rsen and P. Hvelplund, J.<br />
Phys. B : Atom. Mol. Phys., 7, 132, (1974).<br />
[4] M. H. Rees. Physics and Chemistry of the<br />
Upper Atmosphere. Cambridge Atmospheric<br />
and Space Science Series. (1989).<br />
[5] Weihong Liu and D. R. Schultz, The Astrophysical<br />
Journal, 530 :500-503, (2000).<br />
[6] Jürgen Kiefer, Biological Radiation Effects,<br />
Springer-Verlag, (1990).<br />
150<br />
210<br />
120<br />
240<br />
90<br />
270<br />
60<br />
300<br />
30<br />
330<br />
0<br />
78 Valparaíso, Chile
SEPD (u.a.)<br />
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Doble Ionización <strong>de</strong> Helio por impacto <strong>de</strong> iones:<br />
Influencia <strong>de</strong> la Carga <strong>de</strong>l Proyectil<br />
S. D. López 1 , S. Otranto 2 , C. R. Garibotti 1<br />
1 CONICET y Centro atómico Bariloche, Av. Bustillo Km 9.4,8400 S. C. <strong>de</strong> Bariloche, Argentina<br />
2<br />
CONICET y Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> Nacional <strong>de</strong>l Sur, 8000 Bahía Blanca, Argentina<br />
email: sebastlop@gmail.com<br />
En la última década, la técnica COL-<br />
TRIMS (Cold Target Recoil-Ion Momentum<br />
Spectroscopy) ha permitido realizar diversos<br />
procesos <strong>de</strong> colisiones atómicas y moleculares<br />
a un nivel cinemáticamente completo [1].<br />
En particular, se han presentado secciones<br />
plenamente diferenciales (SEPD) para el proceso<br />
<strong>de</strong> doble ionización <strong>de</strong> He por impacto<br />
<strong>de</strong> protones y electrones [2,3]. En esta última<br />
referencia, se comparan las secciones plenamente<br />
diferenciales obtenidas mediante protones<br />
<strong>de</strong> 6 MeV como proyectil con los obtenidos<br />
mediante el impacto <strong>de</strong> electrones <strong>de</strong> 2<br />
keV encontrando diferencias sustanciales en<br />
las estructuras para ambos casos.<br />
En el presente trabajo se analiza en<br />
forma teórica la influencia <strong>de</strong> la carga <strong>de</strong>l<br />
proyectil en el proceso <strong>de</strong> ionización doble <strong>de</strong><br />
Helio por impacto <strong>de</strong> protones y antiprotones<br />
para energías <strong>de</strong> impacto entre 700keV y<br />
6MeV. El estudio se realiza para secciones<br />
eficaces completamente diferenciales. La<br />
configuración elegida para la observación es<br />
aquella en el cual todas las partículas salen en<br />
el plano <strong>de</strong> colisión, observando la distribución<br />
en los ángulos polares electrónicos. Se<br />
emplea el formalismo <strong>de</strong> la primera aproximación<br />
<strong>de</strong> Born en la interacción proyectilblanco.<br />
Como es sabido, esta aproximación<br />
no presenta diferencias ante la carga <strong>de</strong>l proyectil,<br />
y por ello se ha incluido un apantallamiento<br />
dinámico para incluir sus efectos [4].<br />
Para la <strong>de</strong>scripción <strong>de</strong>l sistema atómico<br />
inicial se han utilizado funciones <strong>de</strong>l tipo<br />
Bonham y Kohl que introducen correlación<br />
angular, mientras que para el estado final se<br />
ha utilizado la función <strong>de</strong> onda C3 [5] con<br />
cargas apantalladas como propusieran Berakdar<br />
y Briggs [6]. La introducción <strong>de</strong> este<br />
apantallamiento dinámico logra disminuir la<br />
sobreestimación <strong>de</strong> la distorsión Coulombiana<br />
repulsiva entre los electrones que es dominante<br />
a bajas energías <strong>de</strong> impacto.<br />
3.0x10 -5 protón<br />
antiprotón<br />
2.5x10 -5<br />
1<br />
=0º<br />
2.0x10 -5<br />
1.5x10 -5<br />
1.0x10 -5<br />
5.0x10 -6<br />
0.0<br />
-90 -60 -30 0 30 60 90 120 150 180 210 240 270<br />
2<br />
(grados)<br />
Figura 1. SEPD para la doble ionización <strong>de</strong> He<br />
por impacto <strong>de</strong> protones y antiprotones a 700<br />
keV. Las energías <strong>de</strong> los electrones emitidos son<br />
E 1 = E 1 =10 eV y el momento transferido Q = 0.7<br />
a.u.<br />
References<br />
[1] R. Moshammer et al, NIMB 108, 425 (1996).<br />
[2] A. Dorn et al, Phys. Rev. Lett 86, 3755<br />
(2001).<br />
[3] D. Fischer et al, Phys. Rev. Lett 90, 243201<br />
(2003).<br />
[4] G. Gasaneo, S. Otranto, K. V. Rodríguez,<br />
Proceedings of the XXIV ICPEAC, 369 (2006)<br />
[5] C. R. Garibotti y J. E. Miraglia, Phys. Rev. A<br />
21, 572 (1980).<br />
[6] J. Berakdar y J. S. Briggs, Phys. Rev. Lett.<br />
72, 3799 (1994).<br />
79 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Lα, Lβ, and Lγ x-ray production cross sections of Sm, Dy, Ho, and Tm<br />
by electron impact. Distorted-wave calculations vs experiment<br />
José M. Fernán<strong>de</strong>z-Varea 1 , Silvina Segui 2 and Michael Dingfel<strong>de</strong>r 3<br />
1<br />
Facultat <strong>de</strong> <strong>Física</strong> (ECM and ICC), Universitat <strong>de</strong> Barcelona, Diagonal 647, E-08028 Barcelona, Spain<br />
2<br />
Centro Atómico Bariloche (CNEA), 8400 San Carlos <strong>de</strong> Bariloche, Río Negro, Argentina<br />
3<br />
Department of Physics, East Carolina University, Greenville, North Carolina 27858, United States of America<br />
email address corresponding author: jose@ecm.ub.es<br />
The ionization of atoms by the impact<br />
of electrons is a fundamental process of<br />
nature. In addition to its interest from the<br />
purely theoretical si<strong>de</strong>, several experimental<br />
techniques require knowledge on the associated<br />
cross sections. For instance, Auger electron<br />
spectroscopy and electron-probe microanalysis<br />
need such input data for quantitative<br />
analysis.<br />
The distorted-wave Born approximation<br />
(DWBA) has become a well-established<br />
formalism to calculate cross sections for the<br />
ionization of atomic inner shells by electron<br />
impact [1-3]. Comparison of DWBA cross<br />
sections with available experimental information<br />
provi<strong>de</strong>s confi<strong>de</strong>nce in the predictions of<br />
this theoretical approach. Nevertheless, a<br />
thorough assessment of the DWBA is still <strong>de</strong>sirable,<br />
especially in the case of the L and M<br />
shells of atoms with intermediate and high<br />
atomic numbers.<br />
In a recent work [4] we studied the<br />
emission (after electron impact) of Lα, Lβ,<br />
and Lγ characteristic x-rays by atoms with 72<br />
≤ Z ≤ 83, paying attention to electron energies<br />
E < 50 keV. Good agreement was generally<br />
found between DWBA x-ray production<br />
cross sections and existing measurements.<br />
The present work is a continuation of<br />
the previous one, focusing now on lanthani<strong>de</strong><br />
atoms. In particular, we investigate the emission<br />
of Lα, Lβ, and Lγ x-rays by elements<br />
Sm, Dy, Ho, and Tm, whose respective atomic<br />
numbers are 62, 66, 67, and 69. To this<br />
end, DWBA cross sections for the ionization<br />
of the L 1 , L 2 , and L 3 shells of the consi<strong>de</strong>red<br />
atoms were calculated on a <strong>de</strong>nse grid of<br />
electron kinetic energies. This was done solving<br />
numerically the radial Dirac equation for<br />
the bound and free wave functions of the projectile<br />
and active electrons in a Dirac-Fock-<br />
Slater potential, and summing the required<br />
partial-wave series. Atomic relaxation parameters<br />
(i.e. fluorescence yields, Coster-Kronig<br />
and radiative transition probabilities,<br />
emission rates) were then employed to evaluate<br />
the sought Lα, Lβ, and Lγ x-ray production<br />
cross sections. Three sets of relaxation<br />
parameters were adopted, namely those used<br />
in reference [4] as well as the values from the<br />
Evaluated Atomic Data Library [5].<br />
The resulting x-ray emission cross sections<br />
are rather insensitive to the specific<br />
choice of relaxation data set. The predictions<br />
of the DWBA are in reasonable agreement<br />
with measurements reported in the literature<br />
[6-8], especially for Dy and Tm. As an example,<br />
figure 1 shows the comparison<br />
between theoretical and experimental cross<br />
sections of Dy. However, the experimental<br />
values are systematically lower than the theoretical<br />
ones, with Sm displaying the largest<br />
disagreement.<br />
The observed discrepancies might be<br />
partly caused by shortcomings of the correction<br />
applied to the raw experimental data to<br />
account for the finite thickness of the sample<br />
and the presence of the thick substrate. These<br />
effects tend to increase the production of x-<br />
rays above the values that would be measured<br />
if the sample were a thin, self-supporting<br />
foil. Multiple-scattering theories might be inappropriate<br />
to estimate these corrections at<br />
the consi<strong>de</strong>red low energies.<br />
80 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
[2] J. Colgan, C. J. Fontes, and H. L. Zhang,<br />
Phys. Rev. A 73, 062711 (2006).<br />
[3] D. Bote and F. Salvat, Phys. Rev. A 77,<br />
042701 (2008).<br />
[4] J. M. Fernán<strong>de</strong>z-Varea, S. Segui, and M.<br />
Dingfel<strong>de</strong>r, Phys. Rev. A (submitted).<br />
[5] S. T. Perkins, D. E. Cullen, M. H. Chen, J.<br />
H. Hubbell, J. Rathkopf, and J. Scofield, Tables<br />
and Graphs of Atomic Subshell and Relaxation<br />
Data <strong>de</strong>rived from the LLNL Evaluated Atomic<br />
Data Library (EADL), Z=1-100, Report UCRL-<br />
50400, vol. 30 (Lawrence Livermore National<br />
Laboratory, Livermore, CA, 1991).<br />
[6] C. -J. Gou, Z. -W. Wu, D. -L. Yang, F. -Q.<br />
He, X. -F. Peng, Z. An, and Z. -M. Luo, Chin.<br />
Phys. Lett. 22, 2244 (2005).<br />
[7] Z. -W. Wu, C. -J. Gou, D. -L. Yang, Z. An,<br />
X. -F. Peng, F. -Q. He, and Z. -M. Luo, Chin.<br />
Phys. Lett. 22, 2538 (2005).<br />
[8] Z. Wu, C. Gou, D. Yang, X. Peng, F. He,<br />
and Z. Luo, Chin. Sci. Bull. 51, 1929 (2006).<br />
Figure 1. X-ray production cross sections of Dy as a<br />
function of energy. The continuous curves correspond<br />
to theoretical cross sections obtained with relaxation<br />
data taken from the EADL [5]. Symbols are<br />
experimental values from reference [6].<br />
References<br />
[1] S. Segui, M. Dingfel<strong>de</strong>r, and F. Salvat, Phys.<br />
Rev. A 67, 062710 (2003).<br />
81 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Estudio <strong>de</strong> po<strong>de</strong>r <strong>de</strong> frenado <strong>de</strong> partículas α en películas <strong>de</strong>lgadas <strong>de</strong> cobre<br />
en el intervalo <strong>de</strong> energía entre 1,0 a 2,0 MeV.<br />
Roberto Hauyón 1 , German Kremer 2 , Pedro Miranda 2 y J. Roberto Morales 1 , 2 .<br />
1 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> Ciencias, <strong>Universidad</strong> <strong>de</strong> Chile, Casilla 653, Santiago, Chile.<br />
2 Centro <strong>de</strong> <strong>Física</strong> Experimental, CEFEX, Facultad <strong>de</strong> Ciencias, <strong>Universidad</strong> <strong>de</strong> Chile, Casilla 653, Santiago, Chile.<br />
Correo electrónico <strong>de</strong>l autor : rhauyon@gmail.com<br />
El objetivo <strong>de</strong> este trabajo fue el medir el po<strong>de</strong>r<br />
<strong>de</strong> frenado <strong>de</strong> partículas α en el rango <strong>de</strong> energías<br />
entre 1,0 a 2,0 MeV en el acelerador <strong>de</strong> partículas<br />
Van <strong>de</strong> Graaff KN3750 <strong>de</strong> la Facultad <strong>de</strong> Ciencias,<br />
<strong>Universidad</strong> <strong>de</strong> Chile. La principal motivación <strong>de</strong>l<br />
estudio es que en la actualidad existe discrepancia<br />
entre varios grupos y autores en sus datos experimentales<br />
<strong>de</strong> po<strong>de</strong>r <strong>de</strong> frenado <strong>de</strong>l cobre en estos rangos <strong>de</strong><br />
energías con las partículas α. Se contrastó los datos<br />
obtenidos con la teoría <strong>de</strong> Bethe-Bloch, calculadas<br />
por el programa SRIM, y con otros laboratorios. Se<br />
obtuvo consistencia entre los valores experimentales<br />
con los cálculos propuestos por SRIM.<br />
Actualmente hay un gran interés por conocer<br />
con mejor exactitud varios parámetros nucleares como<br />
secciones eficaces <strong>de</strong> reacciones y po<strong>de</strong>r <strong>de</strong> frenado<br />
[1–9]. En particular, el po<strong>de</strong>r <strong>de</strong> frenado, tiene<br />
varias décadas <strong>de</strong> estudio, tanto a nivel experimental<br />
como a nivel teórico. Dentro <strong>de</strong> estas últimas dos<br />
décadas se han incluido para su estudio técnicas <strong>de</strong><br />
simulación para diversos usos y nuevas metodologías<br />
experimentales. Las motivaciones actuales para<br />
este estudio van <strong>de</strong>s<strong>de</strong> su uso en la física médica,<br />
ciencias espaciales y recientemente [10] en la Comisión<br />
Chilena <strong>de</strong> Energía Nuclear CCHEN, en el <strong>Departamento</strong><br />
<strong>de</strong> Materiales Nucleares y a través <strong>de</strong> un<br />
convenio <strong>de</strong> colaboración con la empresa Sueca<br />
Swedish Nuclear Fuel and Waste Management Co,<br />
(SKB), realiza un estudio <strong>de</strong> la resistencia <strong>de</strong>l cobre<br />
frente a la irradiación y a la corrosión, tanto por factores<br />
químicos como por radiación. Este uso no tradicional<br />
<strong>de</strong> cobre sumado a que Chile es un gran productor<br />
<strong>de</strong> cobre hace aún más atractivo el <strong>de</strong>sarrollo y<br />
la investigación que preten<strong>de</strong> utilizar cobre dopado<br />
con fósforo como blindaje para <strong>de</strong>sechos nucleares <strong>de</strong><br />
alta actividad por emisión <strong>de</strong> partículas α. El cobre es<br />
un material que combina entre muchas cosas, una<br />
buena resistencia a la corrosión, alta conducción<br />
térmica y eléctrica, y atractivas propieda<strong>de</strong>s mecánicas<br />
a temperaturas bajas, ambiente y mo<strong>de</strong>radamente<br />
altas. En países como Suecia [10,11] y Finlandia [10]<br />
se ha seleccionado a los contenedores con pare<strong>de</strong>s <strong>de</strong><br />
cobre como la mejor alternativa para aislar <strong>de</strong>sechos<br />
nucleares <strong>de</strong> alta actividad.<br />
La metodología experimental con la cual se<br />
mi<strong>de</strong> el po<strong>de</strong>r <strong>de</strong> frenado se conoce como método<br />
<strong>de</strong> trasmisión, la cual consiste en la irradiación<br />
<strong>de</strong> un blanco <strong>de</strong>lgado <strong>de</strong> cobre mediante un haz<br />
<strong>de</strong> partículas α. El acelerador es capaz <strong>de</strong> proveer<br />
una corriente <strong>de</strong> haz estable <strong>de</strong> 5 nA, el cual traspasa<br />
blancos <strong>de</strong>lgados autosoportantes. Esto nos<br />
permitió, mediante un sistema espectroscópico<br />
apropiado, <strong>de</strong>terminar la perdida <strong>de</strong> energía <strong>de</strong>l<br />
haz <strong>de</strong> partículas al atravesar el material bajo estudio.<br />
Figura 1: Superposición <strong>de</strong> espectros para <strong>de</strong>terminar<br />
la perdida <strong>de</strong> energía ocurrida en 1,82 MeV <strong>de</strong>bido<br />
a la película auto soportante <strong>de</strong> cobre. En el<br />
espectro sin atenuar la energía es 1,82 MeV con<br />
FWHM <strong>de</strong> 20 keV con un total <strong>de</strong> 814 cuentas y<br />
cuentas netas 808 ± 29. En el espectro con la película<br />
auto soportante la energía medida fue 1,65 MeV<br />
con FWHM <strong>de</strong> 35 keV con un área total <strong>de</strong> 789 cuentas<br />
y cuentas netas <strong>de</strong> 789 ± 28. En ambos espectros<br />
el tiempo real <strong>de</strong> medición fue <strong>de</strong> 1200 segundos.<br />
Los blancos son fabricados utilizando la<br />
técnica evaporación disponible en el Laboratorio<br />
82 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
<strong>de</strong> Sólidos <strong>de</strong> la Facultad <strong>de</strong> Ciencias <strong>de</strong> la <strong>Universidad</strong><br />
<strong>de</strong> Chile. La <strong>de</strong>nsidad superficial <strong>de</strong> estos<br />
blancos se <strong>de</strong>terminó mediante la técnica <strong>de</strong><br />
retrodisperción <strong>de</strong> Rutherford.<br />
Figura 2: Espectro RBS <strong>de</strong> partículas α sobre la<br />
película autosoportante <strong>de</strong> cobre utilizada para el<br />
experimento. El programa usado para el análisis <strong>de</strong><br />
este tipo <strong>de</strong> espectros es SIMRA[12], con el cual, se<br />
<strong>de</strong>termino la <strong>de</strong>nsidad superficial <strong>de</strong>l blanco.<br />
Con los procedimientos anteriormente<br />
mostrados, obtuvimos valores <strong>de</strong> po<strong>de</strong>r <strong>de</strong> frenado<br />
<strong>de</strong> partículas alfa sobre cobre. En la figura 3<br />
comparamos los valores obtenidos con los datos<br />
experimentales <strong>de</strong> otros laboratorios y los propuestos<br />
por la teoría <strong>de</strong> Bethe-Bloch[13-15], calculados<br />
por SRIM. [8] Se uso <strong>de</strong> referencia la<br />
base <strong>de</strong> datos disponible <strong>de</strong>l Dr. Helmut Paul [7].<br />
Referencias<br />
[1] W. Chu y D. Powers, Phys. Rev. 187 (1969).<br />
[2] W. Wenzel y W. Whaling, Phys. Rev. 88 (1952).<br />
[3] W. Wenzel y W. Whaling, Phys. Rev. 87 (1952).<br />
[4] D. Powers, W. Chu y P. Bourland, Phys. Rev. 165<br />
(1968).<br />
[5] P. Bourland y D. Powers, Phys. Rev. B 3 (1971).<br />
[6] J. F. Ziegler, J. Applied Physics 85 (1999).<br />
[7] H. Paul, Stopping Power for Light Ions. Graphs,<br />
Data, Comments and Programs<br />
(http://www.exphys.uni-linz.ac.at/stopping/, 2008).<br />
[8] J.Ziegler, J.Biersack, The Stopping and Range of<br />
iones in matter (www.srim.org, 2008).<br />
[9] NIST, Stopping Power and Range Tables for Alpha<br />
Particles (www.physics.nist.gov/PhysRefData/<br />
Star/Text/ASTAR.html, 2010)<br />
[10] CCHEN .<br />
[11] RD y D.-P. 95, Swedish Nuclear Fuel and Waste<br />
Management Co. Stockholm .<br />
[12] M.Mayer, SIMNRA, Users’s Gui<strong>de</strong> (Max-<br />
Planck Institute for Plasmaphysics, Garching Germany,<br />
2002).<br />
[13] H. Bethe, Annalen <strong>de</strong>r Physik 397 (1930).<br />
[14] E. Podgorsak, Radiation Physics for Medical<br />
Physicists, Second Edition (Springer, 2010).<br />
[15] W. R. Leo, Techniques for nuclear and particle<br />
physics experiments (Springer Verlag, 1993).<br />
[16] P. Sigmund, Nuc. Inst. Meth. Phys. Res. B. 85<br />
(1994).<br />
[16] W. Chu, J.W. Maye, M.A. Nicolet, Backscattering<br />
Spectrometry (<strong>Aca</strong><strong>de</strong>mic Press, New York,<br />
1978).<br />
[17] W. Chu, Physics Review A 13 (1976).<br />
[18] G.F.Knoll, Radiation Detection and Measurement<br />
(2a Ed., John Wiley & Sons, 1989).<br />
[20] H.H.An<strong>de</strong>rsen y J.F.Ziegler, Stopping Powers<br />
and Ranges of Ions in Matter (Pergamon press,<br />
1977).<br />
Figura 3: Po<strong>de</strong>r <strong>de</strong> frenado <strong>de</strong> partículas alfa sobre<br />
película <strong>de</strong> cobre autosoportante. La línea continua<br />
representa el cálculo <strong>de</strong>l programa SRIM y los puntos<br />
las mediciones experimentales <strong>de</strong> este trabajo y<br />
<strong>de</strong> otros autores.<br />
83 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Ab-Initio Sturmian method for three-body quantum mechanical problems:<br />
Scattering states and ionizing collisions<br />
A. L. Frapiccini 1 , 5 , J. M. Randazzo 1 , 5 ,<br />
G. Gasaneo 2 , 5 , F. D. Colavecchia 1 , 5 , D. M. Mitnik 3 , 5 and L. U. Ancarani 4<br />
1 División <strong>de</strong> Colisiones Atómicas, Centro atómico Bariloche, San Carlos <strong>de</strong> Bariloche, Río Negro, Argentina.<br />
2 Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> Nacional <strong>de</strong>l Sur, Bahía Blanca, Buenos Aires, Argentina<br />
3 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio and <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> Ciencias Exactas y Naturales,<br />
<strong>Universidad</strong> <strong>de</strong> Buenos Aires C.C. 67, Suc. 28, (C1428EGA) Buenos Aires, Argentina.<br />
4 Laboratoire <strong>de</strong> Physique Moléculaire et <strong>de</strong>s Collisions,Université Paul Verlaine-Metz, 57078 Metz, France.<br />
5 Consejo Nacional <strong>de</strong> Investigaciones Científicas y <strong>Técnica</strong>s (CONICET).<br />
email address corresponding author: randazzo@cab.cnea.gov.ar<br />
In this work we present the general theory to<br />
compute scattering states with a novel abinitio<br />
method[1] based on generalized Sturmians.<br />
These functions are solutions of a<br />
radial Schrödinger equation where the magnitu<strong>de</strong><br />
of a generating potential is assumed<br />
as the eigenvalue, while the energy is a parameter<br />
of the calculation. These Sturmians<br />
are versatile enough to inclu<strong>de</strong> almost any<br />
arbitrary (atomic) asymptotic conditions in<br />
the radial electron coordinates, such as the<br />
outgoing flux conditions for Coulomb potentials<br />
which are the a<strong>de</strong>quate ones for<br />
atomic collisions. The full three body<br />
Schrödinger equation is solved with a Configuration<br />
Interaction expansion of the wave<br />
function in these generalized Sturmians. The<br />
basis set is used to expand the scattering<br />
portion of the total wave function, which<br />
evolves from a separable state composed by<br />
a plane wave and the ground hydrogen state.<br />
By means of the Galerkin method, a linear<br />
system of equations is obtained for the expansion's<br />
coefficients. We show that the<br />
scattering wave function has the appropriate<br />
outgoing behaviour in the radial hyper<br />
spherical coordinate.<br />
Single differential cross section for the simple<br />
problem of atomic ionization by electronic<br />
impact in the S-wave mo<strong>de</strong>l is presented<br />
(see Fig. 1). Our results of the cross<br />
sections at 55 and 54.4 eV inci<strong>de</strong>nt energy<br />
present an excellent agreement compared to<br />
Exterior Complex Scaling results[2] and<br />
Time <strong>de</strong>pen<strong>de</strong>nt calculations from M. S.<br />
Pindzola and F. Robicheaux [3].<br />
Figure 1. Single differential cross section for single<br />
electron-atom ionization in the Temkin-Poet mo<strong>de</strong>l<br />
with different theoretical methods (E=54.4 eV).<br />
Acknowledgements<br />
This work has been supported by PICT 08/0934<br />
of ANPCYT (Argentina), PIP 200901/552 of<br />
Conicet (Argentina), and PGI 24/F049, <strong>Universidad</strong><br />
Nacional <strong>de</strong>l Sur (Argentina).<br />
References<br />
[1] A. L. Frapiccini, J. M. Randazzo, F. D.<br />
Colavecchia and G. Gasaneo, J. Phys. B: At.<br />
Mol. Opt. Phys. 101001 43 (2010).<br />
[2] C. W. McCurdy and T. N. Rescigno, Phys.<br />
Rev. A 56, R4369 (1997).<br />
[3] M. S. Pindzola and F. Robicheaux, Phys.<br />
Rev. A 55, 4617 (1997).<br />
84 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Ionización <strong>de</strong> hidrógeno atómico e iones moleculares H + 2<br />
pulsos láser<br />
R. <strong>de</strong>lla Picca, J. Fiol, P. D. Fainstein<br />
por<br />
Centro Atómico Bariloche e Instituto Balseiro (Comisión Nacional <strong>de</strong> Energía Atómica y Univ. Nacional<br />
<strong>de</strong> Cuyo), 8400 S. C. <strong>de</strong> Bariloche, Río Negro, Argentina.<br />
Consejo Nacional <strong>de</strong> Investigaciones Científicas y <strong>Técnica</strong>s (CONICET), Argentina.<br />
Correo Electrónico: fiol@cab.cnea.gov.ar<br />
El <strong>de</strong>sarrollo reciente <strong>de</strong> pulsos láser<br />
<strong>de</strong> muy corta duración, <strong>de</strong>l or<strong>de</strong>n <strong>de</strong> unos<br />
pocos ato-segundos, con frecuencias en la<br />
región <strong>de</strong>l ultravioleta extremo (XUV) plantea<br />
nuevos <strong>de</strong>safíos a nuestro conocimiento <strong>de</strong> la<br />
dinámica producida por interacciones lásermateria.<br />
En particular, el empleo <strong>de</strong> estos<br />
nuevos láseres necesita un conocimiento <strong>de</strong>tallado<br />
<strong>de</strong> la <strong>de</strong>pen<strong>de</strong>ncia <strong>de</strong> la dinámica en los<br />
parámetros <strong>de</strong>l láser: duración, frecuencias e<br />
intensidad [1].<br />
En esta comunicación investigamos la<br />
ionización por sobre el umbral (Above Threshold<br />
Ionization- ATI) para átomos e iones<br />
moleculares <strong>de</strong> hidrógeno. Los cálculos se realizan<br />
en el marco <strong>de</strong> la teoría <strong>de</strong> Coulomb-<br />
Volkov [2–4] utilizando funciones <strong>de</strong> onda exactas<br />
para <strong>de</strong>scribir al sistema electrón-núcleo<br />
tanto en el estado inicial como en el estado final<br />
[5]. El pulso láser es <strong>de</strong>scripto en la forma<br />
E(t) = E 0 ˆε sin 2 (πt/τ) sin(ω(t − τ/2) + ϕ)<br />
para 0 ≤ t ≤ τ y nulo fuera <strong>de</strong> este rango.<br />
Hemos <strong>de</strong>sarrollado una aproximación tipo<br />
dipolar, que permite <strong>de</strong>sacoplar parte <strong>de</strong>l<br />
cálculo con los <strong>de</strong>talles relevantes al pulso<br />
láser <strong>de</strong> los <strong>de</strong>talles <strong>de</strong> los estados atómicos<br />
y moleculares.<br />
Figura 1. Espectro <strong>de</strong> ionización <strong>de</strong> hidrógeno atómico por acción <strong>de</strong> pulsos láser como función <strong>de</strong> la<br />
duración <strong>de</strong>l pulso.<br />
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En las figuras se comparan los cálculos<br />
realizados con la aproximación Volkov-<br />
Coulomb <strong>de</strong> aquellos realizados en la aproximación<br />
“dipolar”, tanto para hidrógeno<br />
atómico como para iones <strong>de</strong> hidrógeno para<br />
distintos pulsos láser.<br />
Figura 2. Espectro <strong>de</strong> ionización <strong>de</strong> iones <strong>de</strong> hidrógeno <strong>de</strong>bido a pulsos láser <strong>de</strong> distinta duración.<br />
Los espectros <strong>de</strong> ionización <strong>de</strong> iones<br />
moleculares muestran un fondo más alto entre<br />
picos ATI para energías <strong>de</strong> electrones altas.<br />
Los resultados obtenidos muestran que<br />
la aproximación dipolar representa un método<br />
alternativo <strong>de</strong> bajo costo computacional para<br />
el cálculo <strong>de</strong> secciones eficaces diferenciales y<br />
totales <strong>de</strong> ionización <strong>de</strong> blancos atómicos y<br />
moleculares complejos<br />
Referencias<br />
[2] G. Duchateau, E. Cormier, and R. Gayet,<br />
Physical Review A 66, 23412 (2002).<br />
[3] P. A. Macri, J. E. Miraglia, and M. S.<br />
Gravielle, Optical Society of America<br />
Journal B 20, 1801 (2003).<br />
[4] V. D. Rodríguez, P. Macri, and R. Gayet,<br />
Journal of Physics B: Atomic Molecular<br />
and Optical Physics 38, 2775 (2005).<br />
[5] R. Della Picca, P. D. Fainstein, M. L. Martiarena,<br />
and A. Dubois, Physical Review A<br />
75, 032710 (2007).<br />
[1] F. Krausz and M. Ivanov, Review of Mo<strong>de</strong>rn<br />
Physics 81, 163 (2009).<br />
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88 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Canalización cuasiplanar <strong>de</strong> protones energéticos en inci<strong>de</strong>ncia normal sobre<br />
nanotubos <strong>de</strong> carbono <strong>de</strong> pared múltiple<br />
Jorge E. Valdés 1 , Isabel Abril 2 , Cristian D. Denton 2 , P. Vargas 1 , E. Figueroa 1 , Néstor R. Arista 3 , Rafael<br />
Garcia-Molina 4<br />
1 Laboratorio <strong>de</strong> Colisiones Atómicas, <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, UTFSM, Valparaíso 2390123, Chile<br />
2<br />
Departament <strong>de</strong> <strong>Física</strong> Aplicada, Universitat d'Alacant, E-03080 Alacant, España<br />
3 Centro Atómico Bariloche, División Colisiones Atómicas, S.C. <strong>de</strong> Bariloche, Argentina<br />
3<br />
<strong>Departamento</strong> <strong>de</strong> <strong>Física</strong> – Centro <strong>de</strong> Investigación en Óptica y Nanofísica, <strong>Universidad</strong> <strong>de</strong> Murcia,<br />
E-30100 Murcia, España<br />
corresponding author: ias@ua.es<br />
Por sus reducidas dimensiones, así como<br />
por sus singulares propieda<strong>de</strong>s electrónicas, mecánicas<br />
y magnéticas, los nanotubos <strong>de</strong> carbono<br />
(CNT) son materiales <strong>de</strong> gran interés en diversas<br />
áreas <strong>de</strong> la física, ciencia <strong>de</strong> materiales o<br />
biomedicina [1]. Entre sus posibles aplicaciones<br />
po<strong>de</strong>mos citar la fabricación <strong>de</strong> transistores <strong>de</strong><br />
efecto campo, así como memorias y sensores, o<br />
la utilización en materiales <strong>de</strong> alta resistencia<br />
mecánica, tales como puntas para microscopios<br />
<strong>de</strong> fuerza atómica y nano-electrodos para dispositivos<br />
ópticos [2]. A<strong>de</strong>más, <strong>de</strong>bido a que los<br />
nanotubos <strong>de</strong> carbono pue<strong>de</strong>n comportarse como<br />
metales o semiconductores con un ancho <strong>de</strong><br />
banda variable, <strong>de</strong>pendiendo <strong>de</strong> su estructura<br />
(diámetro o quilaridad), y a su tamaño nanométrico,<br />
los CNT son candidatos i<strong>de</strong>ales como materiales<br />
en nanoelectrónica [3].<br />
Por otra parte, está bien establecido que<br />
los haces <strong>de</strong> partículas energéticas (iones y electrones)<br />
son capaces <strong>de</strong> modificar la estructura y<br />
las propieda<strong>de</strong>s <strong>de</strong> los nanotubos <strong>de</strong> carbono <strong>de</strong><br />
forma controlada y con precisión casi atómica<br />
[4], por ello, es importante conocer cómo los<br />
haces <strong>de</strong> partículas energéticas <strong>de</strong>positan energía<br />
en los CNT.<br />
En este trabajo simularemos la interacción<br />
<strong>de</strong> haces <strong>de</strong> protones, con energía E 0 = 10 keV,<br />
al incidir sobre nanotubos <strong>de</strong> carbono <strong>de</strong> pared<br />
múltiple (MWCNT), perpendicularmente a su<br />
eje, tal y como se muestra en la figura 1.<br />
Figura 1<br />
Para ello, utilizaremos una simulación<br />
semiclásica que permite calcular las trayectorias<br />
<strong>de</strong>l proyectil a través <strong>de</strong> un MWCNT. La interacción<br />
<strong>de</strong> los protones con los átomos <strong>de</strong> carbono<br />
<strong>de</strong>l nanotubo se ha mo<strong>de</strong>lado mediante un<br />
potencial empírico repulsivo. La pérdida <strong>de</strong><br />
energía electrónica se incluye a través <strong>de</strong>l mo<strong>de</strong>lo<br />
no lineal <strong>de</strong> funcional <strong>de</strong>nsidad (DFT) para un<br />
gas <strong>de</strong> electrones, junto con la aproximación <strong>de</strong><br />
<strong>de</strong>nsidad electrónica local [5].<br />
Nuestra simulación predice que la distribución<br />
<strong>de</strong> pérdida <strong>de</strong> energía <strong>de</strong> los protones,<br />
medida en la dirección <strong>de</strong> inci<strong>de</strong>ncia, muestra<br />
dos picos bien diferenciados. El pico <strong>de</strong> menor<br />
pérdida <strong>de</strong> energía se atribuye a los protones que<br />
se mueven con gran parámetro <strong>de</strong> impacto, b<br />
(medido <strong>de</strong>s<strong>de</strong> el eje <strong>de</strong>l CNT, tal como se representa<br />
en la fig.1), los cuales han sufrido canalización<br />
cuasiplanar cerca <strong>de</strong> los bor<strong>de</strong>s <strong>de</strong>l na-<br />
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V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
notubo. Por otra parte, el pico <strong>de</strong> pérdida <strong>de</strong><br />
energía elevada correspon<strong>de</strong> a protones que inci<strong>de</strong>n<br />
sobre el nanotubo con parámetros <strong>de</strong> impacto<br />
pequeños.<br />
En la figura 2 se muestra el resultado <strong>de</strong> la<br />
simulación para la distribución energética <strong>de</strong> los<br />
protones a ángulo cero tras atravesar un<br />
MWCNT, con una energía inicial, E 0 =10 keV.<br />
En la simulación consi<strong>de</strong>ramos que el nanotubo<br />
<strong>de</strong> carbono <strong>de</strong> pared múltiple tiene un diámetro<br />
interior <strong>de</strong> 5 nm, un diámetro exterior <strong>de</strong> 27 nm,<br />
y está constituido por 34 capas, ya que la distancia<br />
entre capas es <strong>de</strong> 0.335 nm. En la simulación<br />
se han promediado los resultados obtenidos para<br />
la pérdida <strong>de</strong> energía correspondientes a la rotación<br />
<strong>de</strong>l MWCNT alre<strong>de</strong>dor <strong>de</strong> su eje con respecto<br />
al haz <strong>de</strong> protones, puesto que en este caso<br />
no existe simetría entre las capas <strong>de</strong>l nanotubo<br />
<strong>de</strong>bido a la diferente quiralidad <strong>de</strong> cada capa.<br />
En la figura 3 mostramos la distribución<br />
<strong>de</strong> la <strong>de</strong>nsidad electrónica promedio ρ , evaluada<br />
a través <strong>de</strong>l parámetro r s = [ 3/(4πρ)<br />
] , que<br />
1/ 3<br />
explora el haz <strong>de</strong> protones en su trayectoria a<br />
través <strong>de</strong>l MWCNT, en función <strong>de</strong> su parámetro<br />
<strong>de</strong> impacto, b. La simulación muestra claramente<br />
la correlación existente entre las trayectorias<br />
<strong>de</strong> los protones con parámetro <strong>de</strong> impacto gran<strong>de</strong><br />
(es <strong>de</strong>cir, aquellos que inci<strong>de</strong>n próximos al<br />
bor<strong>de</strong> <strong>de</strong>l MWCNT) y una <strong>de</strong>nsidad electrónica<br />
baja. Este resultado indica que estos proyectiles<br />
experimentan un proceso <strong>de</strong> canalización entre<br />
las capas externas <strong>de</strong>l nanotubo, lo cual hace que<br />
sufran una dispersión angular pequeña. Aunque<br />
estos protones sean minoritarios, la mayoría <strong>de</strong><br />
ellos llegarán al <strong>de</strong>tector (que se encuentra a ángulo<br />
cero), en contra <strong>de</strong> lo que suce<strong>de</strong> para protones<br />
con parámetro <strong>de</strong> impacto pequeño, que<br />
sufren mayor dispersión múltiple.<br />
Por último, <strong>de</strong>bemos remarcar que este<br />
comportamiento <strong>de</strong> la transferencia <strong>de</strong> energía<br />
<strong>de</strong> los protones al MWCNT se <strong>de</strong>be claramente<br />
a su configuración geométrica, efecto que no<br />
aparece en grafito o carbono amorfo.<br />
Referencias<br />
[1] M. S. Dresselhaus, G. Dresselhaus, P. Avouris<br />
(Eds.), Carbon Nanotubes, Synthesis, Structure,<br />
Properties and Applications, Springer, Berlin,<br />
2001.<br />
[2] E. Lidorikis, A. C. Ferrari, Photonics with<br />
multiwall carbon nanotube arrays, ACS Nano 3<br />
(2009) 1238.<br />
[3] R. H. Bauchman, A. A. Zakhidov, W. A. <strong>de</strong><br />
Heer, Carbon Nanotubes - The Route Toward<br />
Applications, Science 297 (2002) 787.<br />
[4] A. V. Krasheninnikov, K. Nordlund, Ion and<br />
electron irradiation-induced effects in nano<br />
structured materials, J. Appl. Phys. 107 (2010)<br />
071301.<br />
[5] J. E. Valdés, P. Vargas, C. Celedón, E.<br />
Sánchez, L. Guillemot, V. A. Esaulov, Electronic<br />
<strong>de</strong>nsity corrugation and crystal azimuthal<br />
orientation effects on energy losses of hydrogen<br />
ions in grazing scattering on a Ag(110) surface,<br />
Phys. Rev. A 78 (2008) 032902.<br />
90 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Bulk plasmon excitation in grazing inci<strong>de</strong>nce ionmetal surface collisions<br />
C.A. Salas 1 , F.A. Gutierrez 1 and H. Jouin 2<br />
1<br />
Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>de</strong> Concepción, Casilla 160C, Concepción, Chile<br />
2<br />
CELIA, Université <strong>de</strong> Bor<strong>de</strong>aux I, 351Cours <strong>de</strong> la Libération 33405 Talence, France<br />
email address corresponding author: fgutierr@u<strong>de</strong>c.cl<br />
Recent result [1] for the angular distribution<br />
of neutralized He + ions, after interaction<br />
with Al(111) surfaces un<strong>de</strong>r grazing inci<strong>de</strong>nce,<br />
seem to indicate that new neutralization processes,<br />
besi<strong>de</strong>s the Auger and the surfaceplasmon<br />
mo<strong>de</strong>s, must be invoked to explain completely<br />
the experimental angular distributions<br />
for that system.<br />
It seems that electron capture with bulk<br />
and/or multipolesurfaceplasmon are good candidates<br />
to increase the agreement between theory<br />
and experiment. Multipolesurfaceplasmon<br />
can be viewed as bulk plasmon of the low electron<br />
<strong>de</strong>nsity surface region as indicated by Baragiola<br />
et al [2].<br />
The objective of our work is to explore<br />
the possibility that bulk plasmons could contribute<br />
in a nonnegligible way to the angular distributions<br />
for the He + /Al(111) system low energies<br />
of the projectile ion. For that purpose we<br />
shall consi<strong>de</strong>r a second or<strong>de</strong>r electron plasmon<br />
(SOEP) interaction potential obtained<br />
within the Bohm Pines (BP) formalism [3],<br />
[4] and which was applied to study transition<br />
probabilities for hydrogen recombination in<br />
high <strong>de</strong>nsity high temperature plasmas, although<br />
it is better suited for the electrons in<br />
metals interacting with an external positive<br />
charge.<br />
As it is well known in BP theory the<br />
electron gas of a metal is mo<strong>de</strong>lled as a set of<br />
“quasielectrons” (which interact through<br />
screened Coulomb potentials) plus a set of<br />
oscillations with the bulk plasmon frequency.<br />
Within the Random Phase Approximation<br />
(RPA) these screened electrons and the bulk<br />
plasmons do not couple, which means that<br />
electrons in the metal cannot emit bulk plasmons.<br />
However in the field of an external ion<br />
the electrons can accelerate until it gets<br />
enough velocity to emit a volume plasmon.<br />
The <strong>de</strong>finition of the SOEP potential allows a<br />
simple interpretation of the physics involved.<br />
It contains: (I) the ionelectron interaction<br />
which makes it possible the increment in velocity<br />
of the electron until the bulk plasmon<br />
can be emitted, and (ii) the pole at<br />
ω=q⋅k+k' which signals the collective excitation<br />
of frequency ω and momemtum q<br />
(with k the initial electron momentum and k'<br />
the transferred momentum).<br />
The SOEP potential can also be applied<br />
to evaluate the probability for bulkplasmon<br />
emission during ionsolid collisions in cases<br />
where the ion penetrates the surface at a velocity<br />
below the threshold for bulkplasmon<br />
emission.<br />
Furthermore, the above physical picture<br />
for bulk plasmon emission makes it possible<br />
to explore the possibility of ion neutralization<br />
with bulkplasmon emission for cases<br />
where the slow ions do not cross the surface<br />
(although they remain close to it for a significant<br />
amount of time) as is in grazing inci<strong>de</strong>nce<br />
collisions. This process appears to be<br />
the analog to the above mentioned surface<br />
plasmon induced ion neutralization mo<strong>de</strong>.<br />
References<br />
[1] H. Jouin and F.A. Gutierrez, Nucl. Instrum.<br />
Methods Phys. Res. B. 267, 561 (2009).<br />
[2] R.A. Baragiola, S.M. Ritzau, R.C. Monreal,<br />
C.A. Dukes, and P. Riccardi, Nucl. Instrum.<br />
Methods Phys. Res. B. 157, 110 (1999).<br />
[3] D. Bohm and D. Pines, Phys. Rev. 92, 609<br />
(1953).<br />
[4] F.A. Gutierrez and M.D. Girar<strong>de</strong>au, Phys.<br />
Rev. A. 42, 936 (1990).<br />
91 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Distribuciones <strong>de</strong> Scattering Multiple y Efectos Angulares en la Pérdida <strong>de</strong><br />
energía <strong>de</strong> Protones y Deuterones en Láminas Delgadas <strong>de</strong> Carbono Amorfo<br />
E. D. Cantero 1,2 , G. H. Lantschner 1 , N. R. Arista 1<br />
1 Centro Atómico Bariloche – Instituto Balseiro, S. C. <strong>de</strong> Bariloche, Argentina<br />
2 Consejo Nacional <strong>de</strong> Investigaciones Científicas y <strong>Técnica</strong>s (CONICET), Argentina<br />
email: arista@cab.cnea.gov.ar<br />
Utilizando un acelerador <strong>de</strong> iones <strong>de</strong><br />
bajas energías, se han medido distribuciones<br />
ángulo-energía <strong>de</strong> protones y <strong>de</strong>uterones luego<br />
<strong>de</strong> atravesar una lámina <strong>de</strong> carbono amorfo<br />
<strong>de</strong> 11nm <strong>de</strong> espesor [1].<br />
Se presentan resultados <strong>de</strong> las distribuciones<br />
angulares (Fig. 1) para H + y D + <strong>de</strong> 4, 6<br />
y 9 keV <strong>de</strong> energía inci<strong>de</strong>nte y su comparación<br />
con cálculos <strong>de</strong> la función <strong>de</strong> scattering<br />
múltiple (FMS) mediante el formalismo <strong>de</strong><br />
Sigmund y Winterbon [2], hallándose un muy<br />
buen acuerdo para los potenciales <strong>de</strong> scattering<br />
tipo Moliere y ZBL.<br />
Se estudió también la <strong>de</strong>pen<strong>de</strong>ncia angular<br />
<strong>de</strong> la pérdida <strong>de</strong> energía <strong>de</strong> los iones<br />
(Fig. 2). Se presentan los resultados experimentales<br />
y cálculos utilizando el mo<strong>de</strong>lo teórico<br />
presentado en [3]. Este mo<strong>de</strong>lo contempla<br />
tres contribuciones principales para la<br />
pérdida <strong>de</strong> energía:<br />
a) Efecto que produce el alargamiento <strong>de</strong> camino<br />
en la pérdida <strong>de</strong> energía inelástica.<br />
b) Efecto <strong>de</strong> la rugosidad <strong>de</strong> la lámina (los<br />
iones dispersados en ángulos pequeños han<br />
atravesado con mayor probabilidad las regiones<br />
más <strong>de</strong>lgadas <strong>de</strong> la lámina).<br />
c) Contribución <strong>de</strong>l mecanismo elástico.<br />
Se observa un muy buen acuerdo con<br />
los resultados experimentales para ambos<br />
proyectiles en todo el rango <strong>de</strong> energías investigado,<br />
ampliando la aplicación <strong>de</strong>l mo<strong>de</strong>lo<br />
<strong>de</strong> la Ref. [3] a nuevas combinaciones proyectiles-blanco.<br />
Figura 1. Distribución angular <strong>de</strong> protones <strong>de</strong> 9 keV<br />
luego <strong>de</strong> atravesar un blanco <strong>de</strong> carbono amorfo <strong>de</strong><br />
11nm. Líneas: cálculos <strong>de</strong> FMS [2] para diferentes<br />
potenciales <strong>de</strong> scattering.<br />
Figura 2. Depen<strong>de</strong>ncia angular <strong>de</strong> la pérdida <strong>de</strong><br />
energía. Líneas: efecto <strong>de</strong> cada una <strong>de</strong> las contribuciones<br />
<strong>de</strong>l mo<strong>de</strong>lo teórico [3], y resultado total.<br />
Referencias<br />
[1] Blanco <strong>de</strong> tipo ultrasmooth, A C F - Metals<br />
Arizona Carbon Foil Inc.<br />
[2] P. Sigmund and K. B. Winterbon, Nucl. Instrum.<br />
Methods 119, 541 (1974).<br />
[3] M. Famá, G. H. Lantschner, J. C. Eckardt, C.<br />
D. Denton, and N. R. Arista, Nucl. Instrum.<br />
Methods B 164, 241 (2000).<br />
92 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Stopping power y Straggling <strong>de</strong> protones en Pd<br />
P. A. Miranda 1 , A. Sepúlveda 1 , E. Burgos 1 , H. Fernán<strong>de</strong>z 1 ,<br />
J. R. Morales 1<br />
1 Depto. <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> Ciencias, <strong>Universidad</strong> <strong>de</strong> Chile, Casilla 653, Santiago, Chile<br />
asepulveda@hotmail.es<br />
La pérdida <strong>de</strong> energía <strong>de</strong> las partículas<br />
cargadas al atravesar un material es un proceso<br />
<strong>de</strong> vital importancia en variados campos <strong>de</strong> la<br />
<strong>Física</strong>, tales como el estudio <strong>de</strong> superficies en<br />
<strong>Física</strong> <strong>de</strong>l Estado Solido, en diagnóstico y<br />
tratamiento en Medicina Nuclear, y su utilización<br />
en las técnicas basadas en haces iónicos<br />
(PIXE, RBS, NRA). Aunque existen diversas<br />
teorías que mo<strong>de</strong>lan a<strong>de</strong>cuadamente este<br />
proceso, la medición <strong>de</strong>l po<strong>de</strong>r <strong>de</strong> frenado (stopping<br />
power cross section) y <strong>de</strong> su straggling <strong>de</strong><br />
energía, permiten validar estas predicciones y<br />
mejorar la exactitud <strong>de</strong> los valores actualmente<br />
aceptados.<br />
En este trabajo se presentan mediciones<br />
<strong>de</strong>l po<strong>de</strong>r <strong>de</strong> frenado y <strong>de</strong> straggling <strong>de</strong> protones<br />
sobre paladio. Las mediciones se llevaron a cabo<br />
en el Laboratorio <strong>de</strong> Haces Iónicos <strong>de</strong> la <strong>Universidad</strong><br />
<strong>de</strong> Chile utilizando un acelerador tipo Van<br />
<strong>de</strong> Graaff, el que genera un haz <strong>de</strong> protones <strong>de</strong><br />
corriente estable (5 nA y <strong>de</strong> 2 mm <strong>de</strong> diámetro)<br />
en un rango <strong>de</strong> energías <strong>de</strong> entre 300 y 3100<br />
keV. Los valores se obtuvieron utilizando la<br />
técnica <strong>de</strong> transmisión [1] sobre láminas <strong>de</strong><br />
paladio <strong>de</strong> 0.39±0.06 µm. Este procedimiento<br />
nos permite <strong>de</strong>terminar en forma indirecta tanto<br />
la sección eficaz <strong>de</strong> stopping power S(E AVG ) <strong>de</strong><br />
protones en paladio como el straggling <strong>de</strong> energía<br />
Ω [2].<br />
Los resultados preliminares <strong>de</strong> S(E AVG )<br />
muestran una clara concordancia tanto con predicciones<br />
semiempíricas [3] como con formulaciones<br />
teóricas [4]. Por otra parte, el straggling<br />
normalizado (Ω/Ω B ) 2 en función <strong>de</strong> la energía<br />
inci<strong>de</strong>nte promedio E AVG muestra un comportamiento<br />
aceptable en relación a las teorías <strong>de</strong><br />
Bohr y Bethe-Livingston [5], especialmente a<br />
energías más altas. Cabe <strong>de</strong>stacar que hasta ahora<br />
no existían datos experimentales <strong>de</strong> stopping<br />
power y straggling para este sistema en el rango<br />
<strong>de</strong> energía mencionado.<br />
Referencias<br />
[1] J. Raisanen et al., Nucl. Instr. and<br />
Meth. B 118, 1 (1996).<br />
[2] G. Sun et al., Nucl. Instr. and Meth. B<br />
256, 586 (2007).<br />
[3] J.F. Ziegler, M.D. Ziegler, J.P. Bierzack,<br />
Nucl. Instr. and Meth. B 268, 1818 (2010).<br />
[4] J.C. Moreno-Marín et al., Nucl. Instr.<br />
and Meth. B 249, 29 (2006).<br />
[5] H. Ammi, S. Mammeri, M. Allab,<br />
Nucl. Instr. and Meth. B 213, 60 (2004).<br />
93 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
ENERGY LOSS OF SLOW HYDROGEN IONS IN<br />
CHANNELING CONDITIONS IN AU SINGLE CRYSTAL<br />
J.D. Uribe, A.M. Calle, C. Celedón, E. A. Figueroa, J. E. Valdés<br />
Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>Técnica</strong> Fe<strong>de</strong>rico <strong>Santa</strong> María, Casilla 110-V, Valparaíso, Chile<br />
juan.uribe@postgrado.usm.cl<br />
The study of the interaction of ions<br />
with monocrystalline and polycrystalline<br />
solids is an active area of physics and a<br />
source of multiple technological applications.<br />
We have investigated experimentally<br />
the energy loss of hydrogen ions transmitted<br />
through the direction of a single crystal<br />
gold thin foil in the low energy range (
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Pérdida <strong>de</strong> energía <strong>de</strong> protones en láminas <strong>de</strong>lgadas <strong>de</strong> carbono amorfo<br />
Celedón 1 , J. E. Valdés 1 , P. Vargas 1 , E. Figueroa 1<br />
1 Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>Técnica</strong> Fe<strong>de</strong>rico <strong>Santa</strong> María, Casilla 110-V, Valparaíso, Chile<br />
carlos.celedon@usm.cl<br />
En este trabajo presentamos resultados<br />
experimentales <strong>de</strong> la pérdida <strong>de</strong> energía <strong>de</strong> protones<br />
en láminas <strong>de</strong>lgadas <strong>de</strong> carbono amorfo. El<br />
objetivo <strong>de</strong> éste estudio es verificar el comportamiento<br />
<strong>de</strong> la pérdida <strong>de</strong> energía en función <strong>de</strong><br />
la velocidad <strong>de</strong>l ión y su comparación con los<br />
escasos datos experimentales existentes. Se ha<br />
medido la pérdida <strong>de</strong> energía <strong>de</strong> protones en<br />
geometría <strong>de</strong> transmisión en el rango <strong>de</strong> bajas<br />
energías (
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
dE/dx (eV/A)<br />
12<br />
11<br />
10<br />
9<br />
8<br />
7<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
DFT r s =1.66 I75<br />
DFT r s =1.57 R95<br />
H + → aC A69<br />
H + → aC O79<br />
H + → aC S08<br />
H + → aC 200 Å<br />
H + → aC 200 Å<br />
H + from H 2<br />
+ → hC 180<br />
Å<br />
H + → hC 225 Å<br />
H + from H 2<br />
+ → hC 225<br />
Å<br />
H + → hC 200 Å<br />
H + > a-C<br />
0<br />
0.0 0.1 0.2 0.3 0.4 0.5 0.6<br />
(a.u.)<br />
Figura 1. Pérdida <strong>de</strong> energía <strong>de</strong> H + sobre láminas <strong>de</strong> carbono amorfo en geometría <strong>de</strong> transmisión.<br />
0,6<br />
0,5<br />
H +<br />
C amorfo<br />
0,4<br />
DFT r s<br />
=1,66<br />
Q (a.u)<br />
0,3<br />
0,2<br />
0,1<br />
0,0<br />
0,0 0,2 0,4 0,6 0,8 1,0<br />
Mean Velocity (a.u)<br />
Figura 2. Constante <strong>de</strong> Frenamiento H + sobre carbono amorfo datos experimentales<br />
DOS [estados/eV]<br />
6 s+p<br />
p<br />
s<br />
3<br />
0<br />
-20 -15 -10 -5 0<br />
E [eV]<br />
Figura 3. Densidad <strong>de</strong> estados <strong>de</strong>l Carbono, energías respecto <strong>de</strong>l nivel <strong>de</strong> Fermi.<br />
96 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Energy losses of H and F ions in grazing scattering on a missing row reconstructed<br />
Au(110) surface<br />
Lin Chen 1,2 , Jorge E.Valdés 3 , PatricioVargas 3 , Jie Shen 1 and Vladimir A.Esaulov 1<br />
1 Instituit <strong>de</strong>s Sciences Moléculaires d’Orsay, bât 351, Université <strong>de</strong> Paris Sud, Orsay 91405, France<br />
2 School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China<br />
3 Department of Physics, <strong>Universidad</strong> Tecnica Fe<strong>de</strong>rico <strong>Santa</strong> Maria, Valparaiso, Casilla 110-V, Chile<br />
Energy loss of low energy ions is<br />
particularly important in relation to<br />
nanoscale materials since current electronic<br />
<strong>de</strong>vices have <strong>de</strong>creasing thicknesses.<br />
However experimental work on ion energy<br />
loss at low energies is not very extensive, in<br />
contrast to theoretical work <strong>de</strong>veloped in<br />
the early sixties and more accurate<br />
approaches using quantum formalisms like<br />
Density Functional Theory (DFT) and<br />
binary collision approximation (BCA). In<br />
recent years, a proper <strong>de</strong>scription of the<br />
electronic structure of the real surface has<br />
been emphasized in the <strong>de</strong>scription of ion<br />
slowing down during scattering on surfaces,<br />
particularly for transition metals like Ag<br />
and Au. The <strong>de</strong>pen<strong>de</strong>nce of<br />
crystallographic orientations of the surface<br />
on energy losses of ions was observed<br />
experimentally, and does not be <strong>de</strong>scribed<br />
well by consi<strong>de</strong>ring an averaged electron<br />
<strong>de</strong>nsity. We thus have <strong>de</strong>veloped an<br />
approach to <strong>de</strong>scribe slowing of ions on<br />
surfaces i.e., Ag (110) surface in conditions<br />
of strongly varying electron <strong>de</strong>nsities.<br />
In scattering of highly charged ions on<br />
surfaces very efficient ion neutralization<br />
occurs and hence slowing down of the<br />
neutralized particles has to be consi<strong>de</strong>red.<br />
Here in or<strong>de</strong>r to test further the mo<strong>de</strong>l we<br />
<strong>de</strong>veloped, we report the main features of<br />
an experimental and theoretical study of the<br />
energy losses of hydrogen and fluorine ions<br />
scattered un<strong>de</strong>r grazing inci<strong>de</strong>nce on a<br />
Au(110) surface for various crystalline<br />
directions. We chose the Au(110) surface<br />
since it displays a missing row<br />
reconstruction and is thus highly<br />
corrugated. The semi-classical simulation is<br />
consistent with experiment and reveals that<br />
various trajectory classes correspond to<br />
different contributions in the energy-loss<br />
spectra for various azimuthal orientations of<br />
the surface. A brief <strong>de</strong>scription of the<br />
apparatus used for the present experiments<br />
is the following . H + ions are produced in a<br />
discharge source using H 2 gas, and fluorine<br />
negative ions are produced using CF 4 . Ions<br />
are mass selected and <strong>de</strong>flected through 10<br />
<strong>de</strong>grees to eliminate photons and neutrals<br />
before entering into the main UHV<br />
chamber. The pressure in the chamber is<br />
typically 5×10 -10 torr. Scattering energy loss<br />
measurements were mainly ma<strong>de</strong> using a<br />
time of flight (TOF) technique, for specular<br />
scattering conditions with an inci<strong>de</strong>nt angle<br />
of 3.5° as measured with respect to the<br />
surface plane. The azimuthal angle is<br />
<strong>de</strong>fined as an angle in the surface plane<br />
relative to a given miller-in<strong>de</strong>x<br />
crystallographic direction as shown in<br />
Fig.1. TOF spectra were recor<strong>de</strong>d for<br />
various azimuthal angular settings. The<br />
energy losses are <strong>de</strong>termined with respect<br />
to the energy of the inci<strong>de</strong>nt electrically<br />
reflected beam. This corresponds to<br />
scattering with a repulsive voltage applied<br />
to the sample so that the ions do not<br />
un<strong>de</strong>rgo any inelastic processes.<br />
Y (angstrom)<br />
8<br />
6<br />
4<br />
2<br />
0<br />
-2<br />
-4<br />
-6<br />
first layer<br />
second layer<br />
third layer<br />
0 0 [1-10] 70.5 0<br />
[001]<br />
90 0<br />
-8<br />
-15 -10 -5 0 5 10 15<br />
X (angstrom)<br />
Au (110)<br />
Fig.1. Schematic diagram of the Au(110)<br />
surface and the angle nomenclature used in the<br />
paper<br />
97 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Energy-loss spectra measured for some<br />
crystal azimuthal directions are shown in<br />
Figs.2(a,b) and 3(a,b) for hydrogen and<br />
fluorine inci<strong>de</strong>nt ions. In Figs.2(a,b), the<br />
Full-Width-at-Half-Maximum (FWHM) of<br />
scattered beam is consi<strong>de</strong>rably broad and<br />
seems to have a large energy loss tail. The<br />
most striking difference is observed for F<br />
ions scattering with an azimuthal angle of<br />
70.5°, where a double peak structure is<br />
observed in Figs. 3(a,b) for 4 keV but<br />
disappears for 1 keV.<br />
Intensity<br />
relative intensity<br />
150<br />
100<br />
50<br />
0<br />
0 200 400 600 800 1000 1200<br />
1.1<br />
1.0<br />
0.9 (b)<br />
simulation<br />
0.8<br />
experiment<br />
0.7<br />
0.6<br />
1 keV H + -Au(110)<br />
0.5<br />
0.4<br />
azimuthal angle 0 0.3<br />
0.2<br />
0.1<br />
0.0<br />
-50 0 50 100 150 200 250 300 350<br />
Fig. 2. (a) and (b) Energy loss spectra of 4 and 1 keV H +<br />
ions scattered off a Au (110) surface along the indicated<br />
azimuthal direction of 0 0 respectively<br />
intensity<br />
200<br />
150<br />
100<br />
50<br />
(a)<br />
(a)<br />
energy Loss (eV)<br />
experiment<br />
selected total<br />
selected on top of the surface<br />
selected bellow the first layer<br />
4 keV H + -Au(110)<br />
azimuthal angle 0 0<br />
experiment<br />
selected on top of the surface<br />
selected bellow the first layer<br />
4 keV F - -Au(110)<br />
azimuthal angle 70.5 0<br />
electron capture again leads to F - formation.<br />
Here we introduce neutralization<br />
empirically, using theoretical treatments as<br />
a gui<strong>de</strong>line. Electron transfer processes<br />
occur over the characteristic distances of<br />
around Z F =5.0 atomic units from the image<br />
plane for fluorine. A similar range of<br />
distances is assumed for Auger<br />
neutralization of hydrogen. Image charge<br />
effects are “switched off” for neutralized<br />
particles.<br />
The simulated [1, 2] energy loss spectra<br />
are also shown in Figs.2(a,b) and 3(a,b),<br />
which are in good agreement with the<br />
experiment. We furthermore observed a<br />
splitting of the energy loss spectrum into<br />
two components due to two different types<br />
of the trajectory, as shown in Figs.2(c) and<br />
3(c). The trajectory a results from scattering<br />
from the most top layer of the surface and b<br />
from subsurface has a longer effective<br />
length.<br />
Energy-loss spectra of hydrogen and<br />
fluorine ions scattered off a Au (110)<br />
single-crystal surface in grazing scattering<br />
conditions were reported for various<br />
orientations of the surface. We presented<br />
simulations which take into account the<br />
corrugation of the electron <strong>de</strong>nsity<br />
above the surface are in good agreement<br />
with the experimental data.<br />
relative intensity<br />
1.0<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
0 50 100 150 200 250 300 350<br />
(b)<br />
simulation<br />
experiment<br />
1 keV F - -Au(110)<br />
azimuthal angle 70.5 0<br />
0.0<br />
-20 0 20 40 60 80 100<br />
energy loss (eV)<br />
Fig. 3. (a) and (b) Energy loss spectrum of 4 and 1 keV F -<br />
scattering along the 70.5° direction for Au(110)<br />
respectively.<br />
In <strong>de</strong>scribing H + and F - scattering on Au<br />
one should correctly <strong>de</strong>scribe the effect of<br />
the image potential. This implies a correct<br />
<strong>de</strong>scription of electron transfer processesresonant<br />
and Auger neutralization on the<br />
incoming and outgoing path of the<br />
trajectory. We consi<strong>de</strong>r H + neutralization in<br />
the incoming path and in case of F - we<br />
consi<strong>de</strong>r that at large distances (Z> Z F )<br />
when the affinity level is above the Fermi<br />
level electron loss occurs leading to F°<br />
formation, while at small distances, when<br />
the F - level lies below the Fermi level<br />
References<br />
[1] Valdés J E, Vargas P, Celedón C,<br />
Sanchez E, Guillemot L and<br />
Esaulov V A 2008 Phys. Rev. A<br />
78 32902<br />
[2] Valdés J E, Vargas P, Guillemot L<br />
and Esaulov V A 2007 Nucl.<br />
Inst. And Methods B 256 81<br />
98 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Inverse Photoemission Spectroscopy on Graphene<br />
V. <strong>de</strong>l Campo 1 , P. Häberle 1<br />
1 Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>Técnica</strong> Fe<strong>de</strong>rico <strong>Santa</strong> María, Casilla 110-V, Valparaíso, Chile<br />
email address corresponding author: valeria.<strong>de</strong>lcampo@usm.cl<br />
Graphene is composed by sp 2 carbon<br />
atoms which are arranged in a twodimensional<br />
honeycomb lattice. It has been<br />
observed that carriers behave as massless<br />
Dirac fermions; this makes graphene a<br />
promising material for microelectronics. In this<br />
sense, plenty of research has been ma<strong>de</strong> on<br />
graphene electronic structure. It has been<br />
observed that graphene has a single state at the<br />
Fermi energy in which the π and π* bands<br />
cross at the K point of the Brillouin zone [1]. It<br />
was found that when graphene interacts with<br />
another graphene layer a band gap is opened<br />
[2]. It is also reported that when graphene<br />
grows on a metal surface like Ru(0001) there<br />
is a strong chemical bonding and graphene<br />
looses its 2D properties, but when a second<br />
layer is grown in that system, that layer shows<br />
similar properties to isolated graphene<br />
monolayer [3]. All these studies on graphene<br />
electronic structure have been performed with<br />
techniques which allow analysis of graphene<br />
valence band, no specific studies have been<br />
performed to characterize graphene conduction<br />
band.<br />
For graphene growth we heat a<br />
ruthenium cristal above 1000ºC in Ultra High<br />
Vacuum (~10 -10 Torr). We introduce ethylene<br />
(C 2 H 4 ) to the vacuum chamber, reaching a<br />
pressure of 1.5x10 -7 Torr. After a few minutes<br />
we cool the substrate down to 800ºC and<br />
monitor graphene growth with Low Energy<br />
Electron Diffraction (LEED). Once the<br />
graphene covers the substrate we cool down to<br />
room temperature.<br />
To study the unoccupied band<br />
(conduction band) structure of graphene, we<br />
use Inverse Photoemission Spectroscopy (IPS).<br />
This technique consists on impinging electrons<br />
on the sample. The inciding electrons <strong>de</strong>cay<br />
from one unnocupied state to another<br />
(<strong>de</strong>pending on their initial energy). From this<br />
trasitions photons are emmited from the<br />
sample. We perform isocromat IPS, <strong>de</strong>tecting<br />
only the photons that leave the sample with 9.5<br />
eV. Through the analysis of the photon<br />
intensity as a function of electrons initial<br />
energy we get an insight on the conduction<br />
band of the sample.<br />
Figure 1. Experimental set up for Inverse<br />
Photoemission Spectroscopy. Photons are emitted<br />
after the interaction between electrons and the<br />
sample, only photons with 9.5 eV are <strong>de</strong>tected.<br />
References<br />
[1] S. Marchini, S. Günther, and J. Wintterlin,<br />
Phys. Rev. B 76, 075429 (2007).<br />
[2] T. Ohta, A. Bostwick, J. L. McChesney, T.<br />
Seyller, K. Horn and E. Rotenberg, PRL 98,<br />
206802 (2007).<br />
[3] P. W. Sutter, J. I. Flege and E. A. Sutter,<br />
Nature Materials, 7, 406-411 (2008).<br />
99 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Elemental analysis of the Chaitén volcano ash 2008-2009 eruptions<br />
Shimrit Elimelech, Jorge E. Valdés, P. Vargas<br />
Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>Técnica</strong> Fe<strong>de</strong>rico <strong>Santa</strong> María, Casilla 110-V, Valparaíso, Chile<br />
Shimrit.elimelech@usm.cl<br />
The Chaitén volcano eruptions in 2008 and 2009<br />
have provi<strong>de</strong>d a significant opportunity to study<br />
the typical heavy elemental content and microstructure<br />
of the ash emitted from one of the most<br />
critical volcanoes in Chile. Recent studies of<br />
Chaitén offer insights about the environmental<br />
effects of the 2008 eruption in the water, vegetation<br />
and air. In this study, we offer new insights<br />
about typical properties of the ash such as composition<br />
and microstructure. This information<br />
allows us un<strong>de</strong>rstanding of the process leading<br />
the eruption phenomena, explaining its effects<br />
and predicting the eruption future consequences.<br />
Microstructure Characterization was done using<br />
scanning electron microscopy (SEM) with<br />
mo<strong>de</strong>s of backscattered electrons (BSE) and<br />
secondary electrons (SE). The elements' content<br />
was found using Scanning electron microscopy–<br />
energy dispersive x-ray spectroscopy (SEM-<br />
EDS) and x-ray diffraction (XRD).<br />
First characterization of the first eruption ash<br />
shows that the ash is highly angular with termination<br />
of needles as is clearly shown in figures 1<br />
and 2. This result corresponds to recent observations,<br />
which were done in 2008 [1].<br />
The microstructure of the first eruption ash can<br />
be characterized mostly by fine grain size particles<br />
(d>4um). It has different shapes,<br />
from glass shard like structures to almost spherical<br />
particles.<br />
However, this fine ash microstructure is consi<strong>de</strong>red<br />
to be the greatest health hazard since it can<br />
pass into the lungs, leading to respiratory illnesses<br />
[2]. In addition, it can easily cause ash resuspension<br />
over large areas behind the immediate<br />
region of the eruption.<br />
On the other hand, the microstructure of the second<br />
eruption ash, as it is observed in figure 3,<br />
reflects a very violent eruption consisting of<br />
rocks, chunks and pyroclastic flows. This microstructure<br />
contains various types of crystals with<br />
difference in their geometry and size. It can easily<br />
be observed that the grains size is varying<br />
from hundreds to 500um. However, some grains<br />
show a shard like structure, others have porous<br />
and rough surfaces as can be seen in figures 3-5.<br />
These may indicate something about the eruption<br />
mechanism; a morphology consisting of<br />
pores usually indicates the expansion of gas<br />
bubbles during the eruption.<br />
.<br />
Figure 1. Backscattered electron (BSE) SEM micrograph<br />
of the first eruption ash.<br />
100 Valparaíso, Chile
∗<br />
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Needles<br />
Counts (a.u)<br />
10000<br />
8000<br />
6000<br />
4000<br />
2000<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗ ∗<br />
∗ ∗ ∗<br />
∗ ∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗ SiO 2<br />
∗ Al 2 O 3<br />
∗ K 2 O<br />
∗ Na 2 O<br />
∗<br />
∗<br />
∗<br />
0<br />
20 40 60 80<br />
2θ (<strong>de</strong>gree)<br />
Figure 2. Secondary electron (SE) SEM micrograph<br />
of the first eruption ash.<br />
Figure 4. x-ray diffraction of first eruption ash.<br />
Pores<br />
25000<br />
20000<br />
∗<br />
∗ SiO 2<br />
∗ Al 2 O 3<br />
∗ Na 2 O<br />
Counts (a.u)<br />
15000<br />
10000<br />
Rough<br />
Surface<br />
5000<br />
0<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
∗<br />
20 40 60 80<br />
2θ (<strong>de</strong>gree)<br />
Figure 3. Backscattered electron (BSE) SEM micrograph<br />
of the second eruption ash.<br />
The element contents were similar for both sets<br />
of the ashes' specimens. The main concentrations<br />
referred to are SiO 2 and Al 2 O 3 , while<br />
Na 2 O, K 2 O, FeO, CaO and MgO were found in<br />
small quantities. No significant amounts of Arsenic<br />
were found.<br />
Figures 4 and 5 present XRD patterns acquired<br />
from the first and the second eruptions' typical<br />
ash specimens, respectively. Reflections of SiO 2 ,<br />
Al 2 O 3, K 2 O and Na 2 O confirm the presence of<br />
the phases that were found using EDS.<br />
Figure 5. x-ray diffraction of second eruption ash.<br />
References<br />
[1] J Horwell, C.J., Michnowicz, S., Le Blond,<br />
J., 2008. Report on the mineralogical and geochemical<br />
characterisation of Chaitén ash for the<br />
assessment of respiratory health hazard. International<br />
Volcanic Health Hazard Network(IVHNN)<br />
report(available from<br />
www.ivhhn.org).<br />
[2] Watt, S.F.L.; et al., (2009). Fallout and distribution<br />
of volcanic ash over Argentina following<br />
the May 2008 explosive eruption of Chaiten,<br />
Chile. 114. Journal of Geophysical Research.<br />
101 Valparaíso, Chile
Intensida<strong>de</strong><br />
Intensida<strong>de</strong><br />
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Múltipla ionização <strong>de</strong> Neônio em coincidência com íons <strong>de</strong> B 2 + no regime <strong>de</strong><br />
energia <strong>de</strong> poucos MeV<br />
W. Wolff 1 , H. M. R. <strong>de</strong> Luna 1 , A.C. F. dos Santos 1 , e E. C. Montenegro 1<br />
G.M. Sigaud 2<br />
C.C.Montanari 3,4 , e J.E.Miraglia 3,4<br />
1 Instituto <strong>de</strong> <strong>Física</strong>, Universida<strong>de</strong> Fe<strong>de</strong>ral do Rio <strong>de</strong> Janeiro, Rio <strong>de</strong> Janeiro, Brasil<br />
2 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Pontifícia Universida<strong>de</strong> Católica, Rio <strong>de</strong> Janeiro, Brasil<br />
3 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio, Buenos Aires, Argentina<br />
4 <strong>Departamento</strong> <strong>de</strong> <strong>Física</strong>, Facultad <strong>de</strong> Ciencias Exactas y Naturales, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Buenos Aires,<br />
Argentina<br />
wania@if.ufrj.br<br />
A técnica <strong>de</strong> coincidência projétil-íon<br />
<strong>de</strong> recuo e electron- íon <strong>de</strong> recuo foi utilizada<br />
para investigar a múltipla ionização e os processos<br />
<strong>de</strong> transferência <strong>de</strong> carga em colisões<br />
<strong>de</strong> Boro parcialmente blindado B 2+ com átomos<br />
<strong>de</strong> Neônio na faixa <strong>de</strong> energia <strong>de</strong> 1 até 4<br />
MeV. As experiências foram realizadas usando<br />
o recém <strong>de</strong>senvolvido sistema experimental<br />
baseado em um espectrômetro <strong>de</strong> massa<br />
por tempo <strong>de</strong> vôo que permite <strong>de</strong>tecção tanto<br />
dos elétrons ejetados como dos íons <strong>de</strong> recuo<br />
em coincidência com os projéteis em seus<br />
diferentes estados <strong>de</strong> carga finais coletados<br />
por um <strong>de</strong>tector sensível à posição e/ou barreira<br />
<strong>de</strong> superfície. Um exemplo típico <strong>de</strong><br />
espectro <strong>de</strong> íons <strong>de</strong> recuo correspon<strong>de</strong>ndo a<br />
todos os canais <strong>de</strong> ionização (coincidência<br />
elétron-íon <strong>de</strong> recuo) e ao canal <strong>de</strong> ionização<br />
direta (coincidência íon <strong>de</strong> recuo-B 2+) a uma<br />
energia <strong>de</strong> 2 MeV está ilustrado na figura 1a<br />
e 1b respectivamente. O espectro <strong>de</strong> posição<br />
dos projéteis espalhados na colisão com estados<br />
<strong>de</strong> carga finais B 1, 2 e 3+ está mostrado na<br />
figura 1c.<br />
A contribuição relativa para a ionização<br />
total como para cada um dos processos <strong>de</strong><br />
ionização em estudo (ionização direta, captura<br />
e perda eletrônica simples) na produção<br />
dos íons <strong>de</strong> recuo do Neônio com estados <strong>de</strong><br />
carga q=1-5 foi investigada. A <strong>de</strong>pendência<br />
do estado <strong>de</strong> carga médio do íon <strong>de</strong> recuo<br />
para os diferentes canais foi verificada<br />
em função da energia do projétil inci<strong>de</strong>nte.<br />
As secções <strong>de</strong> choque absolutas totais [1] e<br />
parciais são comparadas com mo<strong>de</strong>los teóricos<br />
e apresentam uma boa concordância qualitativa.<br />
Os dados <strong>de</strong> B 2+ - Ne são também<br />
comparados com o sistema <strong>de</strong> colisão C 3+ -<br />
Ne [2] por ambos íons inci<strong>de</strong>ntes serem isoeletrônicos<br />
com configuração eletrônica (1s 2<br />
2s), tipo lítio.<br />
140<br />
70<br />
0<br />
400<br />
200<br />
0<br />
Ne 5+ Ne 4+ Ne 3+ Ne 2+<br />
20 Ne 1+<br />
22 Ne 1+<br />
200 400 600 800<br />
22 Ne 1+ 20 Ne 1+<br />
Ne 2+<br />
(a)<br />
1000 1200 1400 1600<br />
Canal<br />
Ne 3+<br />
(c)<br />
Figure 1. Espectro <strong>de</strong> Ne q+ para (a) ionização total<br />
(b) ionização direta (c) Espectro dos projéteis<br />
Referências<br />
[1] W. Wolff, H. Luna, A.C.F.Santos and E.C.<br />
Montenegro, Phys. Rev. A 80, 032703 (2009)<br />
[2] T. Kirchner, A.C.F. Santos, H. Luna, M.M.<br />
Sant´Anna, W.S. Melo, G.M. Sigaud, and E.C.<br />
Montenegro, Phys. Rev. A 72, 012707 (2005)<br />
Ne 4+<br />
Ne 5+<br />
(b)<br />
102 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Índice <strong>de</strong> autores<br />
Abril, I...................................................... 36, 44, 59, 89<br />
Alessi, M.................................................................. 75, 77<br />
Amaral, L................................................................ 17, 72<br />
Ancarani, L. U...................................................... 15, 84<br />
Appel, L............................................................................ 72<br />
Archubi, C. D................................................................. 65<br />
Arista, N. R.......................................... 49, 59, 89, 92<br />
Azevedo, G..................................................................... 51<br />
Barrachina, R. O.......................................................... 28<br />
Bernardi, G. ........................................................... 28, 42<br />
Bocán, G.......................................................................... 32<br />
Boufleur, L. A................................................................. 17<br />
Bringa, E. ......................................................................... 18<br />
Burgdörfer, J. .................................................................. 38<br />
Burgos, E.......................................................................... 93<br />
Calle, A. M...................................................................... 94<br />
Cantero, E. D................................................................ 92<br />
Celedón, C. ............................................................ 94, 95<br />
Champion, C. ....................................................... 52, 67<br />
Chen, L.............................................................................. 97<br />
Colavecchia, F. D. ..................................... 15, 26, 84<br />
<strong>de</strong> Barros, A. L. F......................................................... 70<br />
<strong>de</strong> Jesus, V. L. B................................................... 47, 70<br />
<strong>de</strong> Luna, H. M. R............................................ 30, 102<br />
<strong>de</strong> Sanctis, M. L........................................................... 68<br />
<strong>de</strong> Souza, C. T..................................................... 34, 72<br />
Debastiani, R........................................................ 17, 72<br />
Deiss, C. ........................................................................... 38<br />
Del Campo, V............................................................... 99<br />
<strong>de</strong>lla Picca, R................................................................. 85<br />
Denton, C. D...................................... 36, 44, 59, 89<br />
Dias, J. F. ...................................... 17, 20, 22, 59, 72<br />
Díez Muiño, R. ............................................................. 32<br />
Dingfel<strong>de</strong>r, M................................................................ 80<br />
dos Santos, A. C. F. ...............................30, 70, 102<br />
Elimelech, S.................................................................100<br />
Emfietzoglou, D...........................................................36<br />
Esaulov, V......................................................25, 54, 97<br />
Fabrim, Z. E...................................................................55<br />
Fadanelli, R. C...............................................................59<br />
Fainstein, P. D......................................................85, 87<br />
Favero, J. M.....................................................................20<br />
Fernán<strong>de</strong>z, H. ...............................................................93<br />
Fernán<strong>de</strong>z-Varea, J. M....................................44, 80<br />
Ferreira, N..............................................................47, 70<br />
Fichtner, P. F. P.............................................................55<br />
Figueroa, E....................................................89, 94, 95<br />
Fiol, J...........................................................................28, 85<br />
Flores, M. .........................................................................54<br />
Focke, P. ................................................28, 42, 75, 77<br />
Fojón, O. A. .................................23, 52, 57, 67, 68<br />
Frapiccini, A. L......................................................15, 84<br />
Fregenal, D..........................................28, 42, 75, 77<br />
Furdyna, J. K...................................................................46<br />
Galassi, M. E. ..............................................52, 67, 73<br />
García-Molina, R. .............................36, 44, 59, 89<br />
Garibotti, C. R................................................................79<br />
Gasaneo, G...................................................15, 26, 84<br />
Gervasoni, J. L................................................................49<br />
Gran<strong>de</strong>, P. L. .......................................19, 22, 55, 59<br />
Gravielle, M. S.............................................31, 32, 65<br />
Gutierrez, F. A...............................................................91<br />
Häberle, P.......................................................................99<br />
Hanssen, J.....................................................23, 52, 67<br />
Hatori, M.........................................................................72<br />
Hauyón, R. ......................................................................82<br />
Incerti, S............................................................................67<br />
Iochims dos Santos, C. E. ..............................17, 72<br />
103 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Jouin, H............................................................................. 91<br />
Kremer, G........................................................................ 82<br />
Kyriakou, I. ...................................................................... 36<br />
Lamour, E........................................................................ 38<br />
Lantschner, G. H......................................................... 92<br />
Lekadir, H. ............................................................. 52, 67<br />
Liu, X.................................................................................. 46<br />
López, S. D..................................................................... 79<br />
Luce, F. P. ........................................................................ 55<br />
Machado, G................................................................... 19<br />
Martín, F. ......................................................................... 73<br />
Mello, S. L. A.................................................................. 46<br />
Melo, W. S...................................................................... 50<br />
Men<strong>de</strong>s, J. B. S. ............................................................ 46<br />
Menezes, R. S............................................................... 70<br />
Miraglia, J. E.....................................30, 31, 39, 102<br />
Miranda, P. A....................................................... 82, 93<br />
Mišković, Z. L................................................................ 49<br />
Mitnik, D........................................................ 15, 26, 84<br />
Montanari, C. C......................................30, 39, 102<br />
Montenegro, E. C.30, 39, 41, 47, 48, 50, 70,<br />
102<br />
Monti, J. M............................................................. 23, 87<br />
Morales, J. R.......................................................... 82, 93<br />
Mowbray, D. J............................................................... 49<br />
Otranto, S............................................................... 75, 79<br />
Papaléo, R. M............................................................... 34<br />
Penello, G. M................................................................. 46<br />
Peretti, D. E.................................................................... 72<br />
Pires, M. P....................................................................... 46<br />
Politis, M. F..................................................................... 68<br />
Prigent, C......................................................................... 38<br />
Radtke, C......................................................................... 19<br />
Ramond, C...................................................................... 38<br />
Ramos, M. M................................................................ 72<br />
Randazzo, J. M........................................... 15, 26, 84<br />
Rappoport, T. G...........................................................46<br />
Reuschl, R........................................................................38<br />
Rivarola, R. D....................23, 52, 57, 67, 73, 87<br />
Rocha, A. B.....................................................................70<br />
Rozet, J.-P.........................................................................38<br />
Salas, C. A. ......................................................................91<br />
Sanchez, D. F. ...............................................................55<br />
Sant’Anna, M. M................................................46, 50<br />
Santos, A. C. F...............................................................50<br />
Schiwietz, G....................................................................38<br />
Segui, S.....................................................................49, 80<br />
Sepúlveda, A..................................................................93<br />
Shah, M. B. ............................................................47, 70<br />
Shen, J................................................................................97<br />
Shubeita, S. M......................................................22, 59<br />
Sigaud, G. M......................................................50, 102<br />
Sigaud, L..................................................................47, 70<br />
Silkin, V. M.......................................................................65<br />
Sinnecker, E. H. C. P.................................................46<br />
Sortica, M. A. ........................................................19, 55<br />
Souza, D. E. R...............................................................46<br />
Souza, V. S.......................................................................72<br />
Stia, C. R..................................................................57, 68<br />
Stori, E. M...............................................................20, 72<br />
Suárez, S. ................................................................28, 42<br />
Tachino, C. ......................................................................73<br />
Tavares, A. C..................................................................48<br />
Thomaz, R. S..................................................................34<br />
Trassinelli, M..................................................................38<br />
Uribe, J. D........................................................................94<br />
Valdés, J. E. ..............................89, 94, 95, 97, 100<br />
Vargas, P............................................89, 95, 97, 100<br />
Vernhet, D.......................................................................38<br />
Vuilleumier, R.................................................................68<br />
Wolff, W. ...........................................30, 47, 70, 102<br />
Yamazaki. Y...................................................................54<br />
104 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Corres electrónicos participantes<br />
Nombre e-mail País<br />
Ana María Calle Arcila agota13@hotmail.com Chile<br />
André Carlos Tavares<br />
andre.tavares@vdg.fis.puc-rio.br Brasil<br />
Andrea Maricel León Sandoval andre.ooh@gmail.com Chile<br />
Andrés Sepúlveda asepulveda@hotmail.es Chile<br />
Carla Eliete Iochims Dos Santos carlaiochims@yahoo.com.br Brasil<br />
Carlos Celedón carlos.celedon@usm.cl Chile<br />
Carlos Roberto Garibotti gari@cab.cnea.gov.ar Argentina<br />
Christophe Champion champion@univ-metz.fr Francia<br />
Claudia Montanari mclaudia@iafe.uba.ar Argentina<br />
Cláudia Telles <strong>de</strong> Souza claudia.telles@ufrgs.br Brasil<br />
Claudio Archubi archubi@iafe.uba.ar Argentina<br />
Cristian Andrés Salas Domínguez crisalas@u<strong>de</strong>c.cl Chile<br />
Dario Ferreira Sanchez dario@if.ufrgs.br Brasil<br />
Dario Mitnik dmitnik@df.uba.ar Argentina<br />
Diego Oyarzo doyarzo@gmail.com Chile<br />
Elis Moura Stori elistori@gmail.com Brasil<br />
Emilio Figueroa emilio.figueroa@usm.cl Chile<br />
Enio Frota da Silveira enio@fis.puc-rio.br Brasil<br />
Erick Burgos P. eoburgos@gmail.com Chile<br />
Esteban Ramos evramos@fis.puc.cl Chile<br />
Esteban Daniel Cantero canteroe@cab.cnea.gov.ar Argentina<br />
105 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Nombre e-mail País<br />
Geraldo Monteiro Sigaud gms@vdg.fis.puc-rio.br Brasil<br />
Gran<strong>de</strong> Pedro Luis gran<strong>de</strong>@if.ufrgs.br Brasil<br />
Hacène Lekadir lekadir@univ-metz.fr Francia<br />
Hugo Milward Riani <strong>de</strong> Luna hluna@if.ufrj.br Brasil<br />
Isabel Abril ias@ua.es España<br />
Joaquín Díaz <strong>de</strong> Valdés jdiaz@u<strong>de</strong>c.cl Chile<br />
Jocelyn Hanssen jocelyn@univ-metz.fr Francia<br />
Johnny Dias jfdias@if.ufrgs.br Brasil<br />
Jorge E. Valdés jorge.val<strong>de</strong>s@usm.cl Chile<br />
Jorge Esteban Miraglia miraglia@iafe.uba.ar Argentina<br />
José María Fernán<strong>de</strong>z-Varea jose@ecm.ub.es España<br />
Jose Roberto Morales rmorales@uchile.cl Chile<br />
Juan David Uribe Vélez juan.uribe@postgrado.usm.cl Chile<br />
Juan Fiol fiol@cab.cnea.gov.ar Argentina<br />
Juan Martín Randazzo juanm.randazzo@gmail.com Argentina<br />
Liana Appel Boufleur Niekraszewicz liana.boufleur@ufrgs.br<br />
Brasil<br />
Lucas Sigaud lucas@if.ufrj.br Brasil<br />
Marcelo Fiori fiori@unsa.edu.ar Argentina<br />
Marcelo Sant'Anna mms@if.ufrj.br Brasil<br />
Marcos Flores mflorescarra@ing.uchile.cl Chile<br />
Maria Luisa Mora Urrutia metalheart19@gmail.com Chile<br />
María Silvia Gravielle msilvia@iafe.uba.ar Argentina<br />
Mariana Alessi alessi@cab.cnea.gov.ar Argentina<br />
106 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
Nombre e-mail País<br />
Marisa Faraggi faraggi@iafe.uba.ar España<br />
Maurício Sortica mau_ufrgs@yahoo.com.br Brasil<br />
Michael Dingfel<strong>de</strong>r dingfel<strong>de</strong>rm@ecu.edu USA<br />
Moni Behar behar@if.ufrgs.br Brasil<br />
Natalia Ferreira natalia@if.ufrj.br Brasil<br />
Omar Fojón fojon@ifir-conicet.gov.ar Argentina<br />
Pablo Fainstein pablof@cab.cnea.gov.ar Argentina<br />
Paulo Fernan<strong>de</strong>s Costa Jobim pjobim@uol.com.br Brasil<br />
Pedro Focke focke@cab.cnea.gov.ar Argentina<br />
Rafael Garcia-Molina rgm@um.es España<br />
Rafaela Debastiani rafa_<strong>de</strong>bas@yahoo.com.br Brasil<br />
Remigio Cabrera-Trujillo trujillo@fis.unam.mx México<br />
Roberto Rivarola rivarola@fceia.unr.edu.ar Argentina<br />
Roberto Hauyón rhauyon@gmail.com Chile<br />
Samir Shubeita samir.shubeita@ufrgs.br Brasil<br />
Sebastián López sebastlop@gmail.com Argentina<br />
Sebastian Otranto sotranto@uns.edu.ar Argentina<br />
Sebastián Godoy Orellana tatangodoy@gmail.com Chile<br />
Silvina Segui segui@cab.cnea.gov.ar Argentina<br />
Valeria <strong>de</strong>l Campo valeria.<strong>de</strong>lcampo@usm.cl Chile<br />
Vicente Salinas Barrera vicente.salinas@usach.cl Chile<br />
Vladimir Esaulov vladimir.esaulov@u-psud.fr Francia<br />
Wania Wolff wania@if.ufrj.br Brasil<br />
107 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
108 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
109 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia<br />
110 Valparaíso, Chile