Cross sections for the interactions of 1 eV-100 MeV electrons in liquid water and application to Monte-Carlo simulation of HZE radiation tracks

High charge (Z) and energy (E) (HZE) nuclei are the main contributors to the uncertainty of radiation risk in space. They ionize a large number of molecules when they interact with matter, initiating a complex succession of events that leads to the radiation track structure. Radiation tracks are often studied by Monte-Carlo simulations that provide detailed information on energy deposition and production of radiolytic species that damage cellular components. These simulations require total and differential elastic and inelastic cross sections. Most ionized electrons have low energy; therefore, most calculations and experiments have been performed on electrons below 1 MeV. Electrons of similar to 1-100 MeV are also produced; they interact with many target molecules when they slow down and determine the radial extension of HZE tracks. Much less work has been done in this energy range. In this paper, a simulation code named RETRACKS uses interaction cross sections (including bremsstrahlung) to calculate the stopping power, range and average energy needed to produce an ion pair (W) for electrons up to 100 MeV. It was also used previously with the RITRACKS program to calculate the radial dose of HZE ions. These cross sections should allow the simulation of higher energy HZE ions, which will help improve our models of space radiation risk.