Abstract
A classical description of electron emission differential ionization cross sections for highly-charged high-velocity ions ($\sim$ 10 a.u.) impinging on water molecules is presented. We investigate the validity of the classical statistical mechanics description of ionization ($\hbar=0$ limit of quantum mechanics) in different ranges of electron emission energy and solid angle, where mechanisms such as soft and binary collisions are expected to contribute. The classical-trajectory Monte Carlo method is employed to calculate doubly and singly differential cross sections for C$^{6+}$, O$^{8+}$ and Si$^{13+}$ projectiles, and comparisons with Continuum Distorted Wave Eikonal Initial State theoretical results and with experimental data are presented. We implement a time-dependent screening effect in our model, in the spirit of mean-field theory to investigate its effect for highly charged projectiles. We also focus on the role of an accurate description of the molecular target by means of a three-center potential to show its effect on differential cross sections. Very good agreement with experiments is found at medium to high electron emission energies.
Highlights
The investigation of inelastic processes involving biological molecules under the impact of highly charged ions is an active field of study, mainly due to its relevance for hadron therapy [1, 2]
These two energies are representative of the main ionization mechanisms, namely the Soft Collision (SC), Two-center Electron Emission (TCEE) and Binary Encounter (BE) processes
We have studied the validity of the classical-trajectory Monte Carlo (CTMC) model as applied to the calculation of SDCS and DDCS for net ionization in fast highly-charged ion collisions with water molecules by comparing results to recent experimental and theoretical data
Summary
The investigation of inelastic processes involving biological molecules under the impact of highly charged ions is an active field of study, mainly due to its relevance for hadron therapy [1, 2]. Electrons ejected from water molecules due to direct ionization by the projectile or due to the Auger effect, will cause secondary interactions with the biological medium. Depending on the electron energies they will lead to further ionization or excitation processes [3]. The microscopic understanding of the whole time evolution of the heavy-ion impact is needed to accurately describe the final energy deposition, which leads to damage to the DNA of the irradiated tumor cell [4]. Monte Carlo codes are used to simulate all these interactions using the differential and total cross sections for the inelastic processes of different projectiles impinging on water molecules [5]
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