A Monte Carlo program for the analysis of low-energy electron tracks in liquid water.

A Monte Carlo code for the event-by-event simulation of electron transport in liquid water is presented. The code, written in C++, can accommodate different interaction models. Currently it implements cross sections for ionizing collisions calculated with the model developed by Dingfelder et al (1998 Radiat. Phys. Chem. 53 1-18, 2008 Radiat. Res. 169 584-94) and cross sections for elastic scattering computed within the static-exchange approximation (Salvat et al 2005 Comput. Phys. Commun. 165 157-90). The latter cross sections coincide with those recommended in ICRU Report 77 (2007). Other included interaction mechanisms are excitation by electron impact and dissociative attachment. The main characteristics of the code are summarized. Various track penetration parameters, including the detour factor, are defined as useful tools to quantify the geometrical extent of electron tracks in liquid water. Results obtained with the present microdosimetry code are given in the form of probability density functions for initial electron kinetic energies ranging from 0.1 to 10 keV. The sensitivity of the simulated distributions to the choice of alternative physics models has been briefly explored. The discrepancies with equivalent simulations reported by Wilson et al (2004 Radiat. Res. 161 591-6) stem from the adopted cross sections for elastic scattering, which determine largely the spatial evolution of low-energy electron tracks.