Ionization cross sections of water clusters as an alternative to liquid phase water: A Geant4-DNA simulation study

Most of Monte Carlo Simulation (MCS) toolkits used to estimate the biological damage induced by radiations in cells consider these latter as composed of single water molecule. In this work, we used the Geant4-DNA MCS toolkit to evaluate the biological damage in cells modeled as clusters of water molecules instead of single water molecule. Increasing the number of molecules in water clusters enable to approximate liquid phase. Total cross sections for the ionization of small water clusters by electron impact are calculated. The first Born approximation is used to describe the collision dynamics where the incident and the scattered electrons are described by plane waves while the ejected electron is described by a Coulomb wave. Electrons belonging to the target molecule are described by a single-center molecular wave function. Using calculated cross sections, a scaling law and a universal curve are extracted to predict cross sections for the ionization of water clusters by single electron impact. These cross sections are implemented in Geant4-DNA to simulate the number of ionizations, mean-free path, range, stopping power, and the number of double and single strand breaks.