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This chapter presents a specific reliability study of some GEANT4-DNA (version 10.02.p01) processes and models for proton transportation considering ultra-thin layers (UTL). The Monte Carlo radiation transport validation is fundamental to guarantee the simulation results accuracy. However, sometimes this is impossible due to the lack of experimental data and, it is then that the reliability evaluation takes an important role. Geant4-DNA runs in an energy range that makes impossible, nowadays, to perform a proper microscopic validation (cross-sections and dynamic diffusion parameters) and allows very limited macroscopic reliability. The chemical damage cross-sections reliability (experiment versus simulation) is a way to verify the consistency of the simulation results which is presented for 2 MeV incident protons beam on PMMA and PVC UTL. A comparison among different Geant4-DNA physics lists for incident protons beams from 2 to 20 MeV, interacting with homogeneous water UTL (2 to 200 nm) was performed. This comparison was evaluated for standard and five other optional physics lists considering radial and depth profiles of deposited energy as well as number of interactions and stopping power of the incident particle.

Impacts of swift heavy ions of different energy loss in amorphous and crystalline Lennard-Jones (LJ) thin films (2–60 nm) were simulated using classical molecular dynamics to study cratering and sputtering in model molecular thin films. Crater size is determined mostly by evaporation and melt flow from the hot ion track, while rim size is determined both by melt flow and by coherent displacement of particles due to the large pressure developed in the excited region, with minor influence of particles from the substrate. Sputtering yields from both crystalline and amorphous samples are similar (including the scaling with energy loss), due to the extremely high temperature and disordered condition of the track region from where most ejected particles originate in the early stages of the track evolution. Cratering, however clearly depends on the crystallinity of the film. Craters and rims are much smaller in crystalline films mainly due to faster energy dissipation, higher stress threshold for plasticity and smaller free-volume in the ordered phase. We also found a large dependence of the induced surface effects on film thickness below a critical thickness value. The pressure pulse due to the ion impact is weaker and cooling of the excited track is more efficient in short tracks, both contributing to the decreased radiation damage efficiency on ultrathin layers. Despite the simplicity of the LJ model, the simulations in the amorphous films reproduce remarkably well several of the experimental features seen recently on polymer thin and ultrathin films irradiated by swift heavy ions. Fil: Gutierres, L. I.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Lima, N.W.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Thomaz, R. S.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Papaléo, R. M.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina

In this paper, the surface effects of individual heavy ions impacting thin polymerlike films were investigated, using molecular dynamics simulations with the finite extensible nonlinear elastic (FENE) potential to describe the molecular chains. The perturbation introduced by the ions in the lattice was modeled assuming that the initial excitation energy in the ion track is converted into an effective temperature, as in a thermal spike. The track was heated only within the film thickness h, leaving a nonexcited substrate below. The effect of decreasing thickness on cratering and sputtering was evaluated. The results were compared to experimental data of thin polymer films bombarded by MeV-GeV ions and to simulations performed with the Lennard-Jones potential. While several qualitative results observed in the experiments were also seen in the simulations, irrespective of the potential used, there are important differences observed on FENE films. Crater dimensions, rim volume, and sputtering yields are substantially reduced, and a threshold thickness for molecular ejection appears in FENE simulations. This is attributed to the additional restrictions on mass transport out of the excited track region imposed by interchain interactions (entanglements) and by the low mobility of the molten phase induced by the spike. Fil: Lima, N. W.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Gutierres, L. I.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Gonzalez, R. I.. Universidad de Chile; Chile Fil: Müller, S.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Thomaz, R. S.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Papaléo, R.M.. Universidade Católica Do Rio Grande Do Sul; Brasil