Monte Carlo simulation of the energy loss of low-energy electrons in liquid water

Abstract

A Monte Carlo code that performs detailed (i.e. event-by-event) simulation of the transport and energy loss of low-energy electrons (approximately 50-10 000 eV) in water in the liquid phase is presented. The inelastic model for energy loss is based on a semi-empirical dielectric-response function for the valence-shells of the liquid whereas an exchange corrected semi-classical formula was used for K-shell ionization. Following a methodology widely used for the vapour phase, we succeeded in parametrizing the dielectric cross-sections of the liquid in accordance with the Bethe asymptote, thus providing a unified approach for both phases of water and greatly facilitating the computations. Born-corrections at lower energies have been implemented in terms of a second-order perturbation term with a simple Coulomb-field correction and the use of a Mott-type exchange modification. Angular deflections were determined by empirical schemes established from vapour data. Electron tracks generated by the code were used to calculate energy- and interaction-point-kernel distributions at low electron energies in liquid water. The effect of various model assumptions (e.g., dispersion, Born-corrections, phase) on both the single-collision and slowing-down distributions is examined.

Geant4 Physics Processes for Microdosimetry Simulation: Design Foundation and Implementation of the First Set of Models

“…Due to the lack of experimental data in liquid water at low energies for this process and the difficulty of addressing the problem theoretically, the approach applied consists of extending elastic models for the free molecule to the liquid phase; this method is also adopted in [35], [36], [37] and [74].…”

“…The total cross sections for excitation are calculated analytically for each discrete transition taking into account a low energy adjustment function [74].…”

“…To improve the software performance, the total cross sections [74] corresponding to each individual shell are computed by interpolating pre-calculated values stored in twodimensional tables; the tables are structured as a grid over energy and momentum transfer values covering the range of applicability of the model.…”

Monte Carlo Simulation of Electromagnetic Interactions of Radiation with Liquid Water in the Framework of the Geant4-DNA Project

“…The total cross sections for excitation for each discrete transition are calculated analytically taking into account a lowenergy adjusting function [19].…”

“…To improve the software performance, the individual shell total cross sections [19] are computed from the interpolation of bi-dimensional pre-calculated tables over energy and momentum transfer.…”