Aca - Departamento de Física - Universidad Técnica Federico Santa ...
Aca - Departamento de Física - Universidad Técnica Federico Santa ... Aca - Departamento de Física - Universidad Técnica Federico Santa ...
V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Multiple ionization cross section (Mb) 10 3 Ar 5+ x 10 -5 10 2 10 1 10 0 10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 Ar + Ar 2+ Ar 3+ x 10 -1 Ar 4+ x 10 -3 Multiple ionization cross section (Mb) C avalcanti D uBois 10 2 Schram for e+Ne Andersen 10 1 10 0 10 -1 10 -2 10 -3 includes K-shell PCI includes L-shell shake off Ne + Ne 2+ Ne 3+ x 10 -1 10 -7 10 2 10 3 Energy (keV/amu) 10 2 10 3 10 4 Energy (keV) Fig. 2 Ionización múltiple de Ar por He+ El acuerdo con los valores experimentales es bueno, en especial para Ar y Kr para ambos iones, H+ y He+. En el caso de H+ en Xe, y He+ en Ar y Kr, comparamos resultados teóricos y valores experimentales hasta ionización quíntuple. Multiple ionization cross sections (Mb) 10 3 Xe + 10 2 Xe 2+ 10 1 10 0 Xe 3+ x 10 -1 10 -1 10 -2 10 -3 Xe 4+ x 10 -3 10 -4 10 -5 Xe 5+ x 10 -5 10 -6 10 2 10 3 Energy (keV/am u) Fig. 3 Ionización múltiple de Xe por H+ Fig. 4 Ionización múltiple de Ne por H+ El caso de Ne muestra características propias (ver figura 4). La única capa que contribuye a aumentar la ionización múltiple directa es la capa K, dado que no hay Auger de 2s y 2p. Sin embargo los resultados teóricos subestiman los valores experimentales dando muestras de que hay algún otro proceso contribuyendo a la doble y triple ionización de Ne. Mostraremos que la inclusión de shake off [7-9] darían la tendencia correcta para describir la ionización múltiple de Ne a altas energías. References [1] Cavalcanti E G, et al J. Phys. B: At. Mol. Opt. Phys. 35 3937 (2002). [2] Spranger T and Kirchner T J. Phys. B: At. Mol. Opt.Phys. 37 4159 (2004). [3] Sigaud G M et al, Phys. Rev. A 69 062718 (2004). [4] Galassi M E, Rivarola R D and Fainstein P D, Phys. Rev.A 75 052708 (2007). [5] Schenk G and Kirchner T, J. Phys. B: At. Mol. Opt. Phys. 42 205202 (2009) [6] Montanari C C, Montenegro E C and Miraglia J E, J. Phys. B: At. Mol. Opt. Phys. 43 165201 (2010). [7] Kochur et al, J. Phys. B: At. Mol. Opt. Phys. 35 395 (2002) [8] Carlson T A and Nestor C W, Phys. Rev.A 8 2887 (1973). 40 Valparaíso, Chile
V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Ionization pattern in the region of the Bragg peak E C Montenegro 1 Instituto de Física, UFRJ, Caixa Postal 68528, Rio de Janeiro, 21945-970, RJ, Brazil. montenegro@if.ufrj.br Regarding direct collisional effects the penetration of heavy ions through matter is usually characterized by the energy loss, from the projectile side, and by the number of ions produced along its trajectory, from the target side. While energy loss measurements are numerous, embracing a large number of combinations of projectiles and targets – the latter mostly solids – ionization measurements by ions with the proper charge states, associated to the energies they have during their way through matter, are rare and restricted to gas targets, due to the nature of these measurements. For a given energy transfer by the projectile there is a large number of dynamical alternatives for a given final state of the target, making the theoretical description of the ionization by heavy ions more complex compared to those of energy loss. This difficulty is enhanced in the region of the Bragg peak where more than one collision channel compete on equal foot. Recently, it was shown that the shape of the Bragg peak is very much due to the energy transfer to inner target electrons [1]. Although the cross section for the removal of inner electrons is small, this process involves large energy transfer. This contrasts with the ionization pattern, which is dominated by the removal of outer electrons with large cross sections and small energy transfers. In this work the differences between the patterns of energy loss and ion production are studied. Available measured cross sections for collisions of heavy ions with noble gases are used as a starting point to estimate the ionization pattern in the velocity region corresponding to the Bragg peak. This estimate requires the inclusion of other - and usually not measured - charge states which contribute to the energy deposition along the particle path in this region. It is found that, in the region of the Bragg peak for energy loss, the ionization pattern is much flatter in shape as compared with that of the energy loss, as shown in Fig.1. This result points in the same direction as that observed in water [2], where essentially no peak was observed in the ion production pattern in the velocity region corresponding to the distal part of the Bragg peak. The knowledge of the shape of the ionization pattern is needed to interpret the effects of radiation damage by heavy ions from medical to technological applications. Figure 1. Cross section for target ions production and number of target ions produced by C ions in water. The shape is not of a single and sharp peak. References [1] E. D. Cantero, R. C. Fadanelli, C. C. Montanari, M. Behar, J. C. Eckhardt, G. H. Landschner, J. E. Miraglia and N. R. Arista, Phys. Rev. A79, 042904 (2009). [2] E. C. Montenegro, M. B. Shah, H. Luna, S. W. J. Scully, A. L. F. de Barros, J. A. Wyer, and J. Lecointre, Phys. Rev. Lett. 99, 213201 (2007). 41 Valparaíso, Chile
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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