Energy loss by non-relativistic electrons and positrons in liquid water

Inelastic collision cross-sections, mean free paths, stopping powers, energy loss distributions, mean energy losses and csda ranges are evaluated for non-relativistic electrons and positrons in liquid water using a formalism in which the response of the medium is expressed employing the experimental dipole oscillator strength distribution. Monte Carlo track structure simulations employing the calculated inelastic collision cross-sections, and elastic cross-sections evaluated using partial wave methods, are used to determine the energy dependence of positron and electron path-lengths, penetrations, and non-homogeneous energy deposition distributions. The calculated data are discussed, and compared and contrasted. The energy loss properties of electrons and positrons that depend only on the differential inelastic collision cross-section are similar for particle energies ≳ 1 keV, but there are apparent differences for lower energies. The energy loss properties depending on the size of the energy transfer events and on the differential inelastic collision cross-section differ for all particle energies. The differences found are the consequence of electron indistinguishability on the inelastic cross-section for the electron. Non-homogeneous energy deposition distributions of positrons with energy less than 1 keV are significantly more forward directed than those of electrons with the same initial energy. The differences are due to the larger inelastic collision cross-section of a positron compared to an electron, and its effect on the relative numbers of inelastic and elastic collisions.