Simulation of the energy spectra of swift light ion beams after traversing cylindrical targets: a consistent interpretation of experimental data relevant for hadron therapy

Abstract

We have performed detailed simulations of the energy spectra, recorded at several angles, of proton and helium ion beams after traversing thin cylindrical targets of different nature (liquid water and ethanol jets, as well as a solid aluminium wire), in order to reproduce a series of measurements intended to assess the stopping power of 0.3-2 MeV ions. The authors of these experiments derived values of the stopping power of liquid water (a quantity essential for the evaluation of radiation effects in materials, particularly for radiotherapy purposes) that are ∼10% lower than what is expected from other measurements and theories. In our simulations, instead of treating the stopping power as an unknown free parameter to be determined, we use as input the electronic stopping power accurately calculated within the dielectric formalism. We take into account in the simulations the different interactions that each projectile can experience when moving through the target, such as electronic stopping, nuclear scattering or electron charge-exchange processes. The detailed geometry of the target is also accounted for. We find that our simulated energy distributions are in excellent agreement with the published measurements when the diameter of the cylindrical targets is slightly reduced, what is compatible with the potential evaporation of the liquid jets. On the basis of such an excellent agreement, we validate the accuracy of the model we use to calculate electronic excitation cross sections for ions in condensed matter in its range of applicability (particularly the electronic stopping power) needed for charged particle transport models, and we offer a consistent, but alternative, interpretation for these experiments on ion irradiation of cylindrical targets. Contribution to the Topical Issue "Dynamics of Systems on the Nanoscale", edited by Ilko Bald, Ilia A. Solov'yov, Nigel J. Mason and Andrey V. Solov'yov.

Experimental electronic stopping cross section of transition metals for light ions: Systematics around the stopping maximum

“…The quantity that describes the resulting average energy loss per unit path length is commonly denoted as the stopping power S = dE/dx of the material for a specific ion, which can, based on the nature of the interaction, be separated into a nuclear and an electronic component [1,2]. The stopping power of matter for ions has been under investigation for over a century [3] and has become a decisive quantity in ion beam analysis [4,5] and fusion research [6,7], as well as medical applications [8,9]. For many of these applications, it is convenient to normalize S by the atomic density n of the material to get rid of the trivial dependence on the material density.…”

Special issue: Dynamics of systems on the nanoscale (2018). Editorial

“…These software packages have been designed to become powerful and universal instruments of computational research in the field of MBN Science, which should play a role of a "virtual microscope" and a "camera" capable to explore, simulate, record and visualize both structure and dynamics of the MBN-world with an atomistic level of accuracy, in order to both reproduce its known features and predict the new ones. In this Topical Issue, many contributions [12][13][14][15][16][17][18][19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][35] provide case studies conducted with these packages and demonstrate their application to a broad variety of topical areas in MBN science as listed at the beginning of this Editorial. To be noted that these universal and powerful software packages are fully applicable to a broad variety of the topical areas of the MBN Science listed above in the introductory part of the Editorial.…”

“…De Vera et al [34] report the results of simulations of energy distributions for swift light ion beams after traversing cylindrical targets of different nature (liquid water and ethanol jets, as well as a solid aluminium wire). These simulations have been performed in order to reproduce a series of measurements intended to assess the stopping power of 0.3-2 MeV ions.…”

Differential scattering in proton collisions with molecular hydrogen

“…The simplest example is proton scattering on molecular hydrogen, which remains an active area of research both experimentally and theoretically. One reason for this is the recent emergence of hadron therapy for cancer treatment [1] where the need for accurate stopping cross sections for ion scattering in biologically relevant molecules is of the utmost urgency [2]. In this modern cancer treatment modality, protons (or heavier ions [3]) are used to bombard the tumour site and destroy cancerous cells.…”