Aca - Departamento de Física - Universidad Técnica Federico Santa ...

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V Encuentro Sud Americano de Colisiones Inelásticas en la Materia In Fig. 1 we display the differential electron emission probability for 100 keV protons impinging grazing on a Be (0001) surface considering three different ejection angles in the scattering plane. Due to the contribution of surface occupied states, electron spectra display pronounced shoulders at intermediate energies, which are not present when the surface is described in a simpler way by employing a finite step potential to respresent the electron surfaceinteraction (Jellium model). These shoulders are also observed for emission out of the scattering plane and their positions are gradually shifted to lower electron energies as the emission angle increases. 10 100 keV H + Be(0001) dP/dk (arb. units.) 1 0.1 0.01 Jellium BSB 1E-3 50 100 150 200 Energy (eV) Figure 2. Total emission spectra for 100 keV protons impinging on a Be(0001) surface. BSB results are compared with Jellium model results. Remarkably, surface state effects completely dissapear when we calculate the total emission probability as a function of the electron energy. These results are shown in Fig. 2. References [1] V.M. Silkin et al, J. Phys.: Condens. Matter 20, 304209 (2008) [2] M. N. Faraggi et al, Phys. Rev. A 69, 042901 (2004) [3] E. V. Chulkov, V. M. Silkin and P. M. Echenique, Surf. Sci. 391, L1217 (1997); 437, 330 (1999) [4] M. N. Faraggi et al, Phys. Rev. A 72, 012901 (2005). 66 Valparaíso, Chile

V Encuentro Sud Americano de Colisiones Inelásticas en la Materia Monte Carlo simulation for proton track structure in biological matter H. Lekadir 1 , C. Champion 1 , S. Incerti 2 , M. E. Galassi 3 , O. Fojón 3 , R. D. Rivarola 3 , and J. Hanssen 1 1 Laboratoire de Physique Moléculaire et des Collisions, Université Paul Verlaine-Metz, Metz, France 2 Université Bordeaux 1, CNRS/IN2P3, CENBG, Bordeaux-Gradignan, France 3 Instituto de Física Rosario, CONICET, Universidad Nacional de Rosario, Rosario, Argentina Corresponding author: lekadir@univ-metz.fr Monte Carlo simulations are well suited for describing the transport of charged particles in matter and more particularly in biological medium for predicting the radio-induced biological consequences. Ion beams are commonly used in radiotherapy essentially due to their physical and radiobiological characteristics which radically differ from those of conventional radiation beams (photons). Nowadays, protons are employed in many countries for treating particular pathologies. Indeed, in comparison to conventional techniques, protons offer an increased biological efficiency and a better ballistic by depositing in particular a large part of their initial energy in a narrow region - at the end of their path- called the Bragg peak region. Then, they allow a better protection of organs at risk in cancer therapy. To model in details the track-structure of protons in biological matter, we have then developed a full-history Monte Carlo code called TILDA2 which is able to describe, step by step, all the proton induced-collisions in biological matter, this latter being alternatively modelled by water and by some of its most important biological entities, namely, the DNA bases. The originality of our code resides in the physical processes that are integrated. Thus, TILDA2 takes into account a large panel of ionizing processes such as single and double ionization and capture, transfer ionization and excitation. To do that, we have first investigated different theoretical models for providing the needed input data, namely, the total cross sections: a first classical one based on a CTMC- COB [1,2] approach and two quantum mechanical ones, namely, a Coulomb Born (CB1) model and a continuum-distorted wave eikonal-initialstate (CDW-EIS) one. All the obtained cross sections have been validated via theory/exp comparisons. TCS (10 -16 cm 2 ) 10 3 a) H 2 O 10 2 10 1 10 0 10 -1 10 -2 10 -3 10 -4 10 2 10 3 10 4 7 Incident energy (keV/u) b) Guanine 10 2 10 3 10 4 Figure 1. Total cross sections of the ionizing processes included into the Monte Carlo code TILDA2 for describing the proton transport in water and guanine. Under these conditions, we have access to a large number of physical quantities such as stopping power, energy deposition, charge fraction, range… in water and DNA components. Then, we have shown that the energy deposit patterns were extremely dependent on the medium description. References [1] H. Lekadir et al., Nucl. Instr. Meth. Phys Res. B 267, 1014 (2009). [2] H. Lekadir et al., Phys. Rev. A 79, 062710 (2009). 67 Valparaíso, Chile

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