Semi-empirical inelastic cross sections for electron transport in liquid water.

Abstract

Electron inelastic cross sections for water in the liquid phase are important for developing Monte Carlo codes that simulate the full degradation of any radiation beam in biological matter. The limited experimental information for condensed targets and the complexity of the background theory has led to largely heuristic semi-empirical models. The present work makes use of the dielectric formalism under the first Born approximation to develop inelastic cross sections for low-energy electron transport in liquid water. A Drude model was used to describe the energy-loss distribution at the dipole limit on the basis of optical data, while the impulse approximation and an empirical generalised-oscillator-strength provided the extension to finite momentum transfer. Born corrections established earlier for water vapour were applied at low impact energies. Core-electron transitions were treated by a binary model with exchange terms. Sum-rules were satisfied to within 1-2% while an 1-value of about 80 eV was obtained. A comparison with other studies is provided.