An approach to Monte Carlo simulation of low-energy electron and photon interactions in air

In this paper we present an approach to an energy deposition model for low energy (10 eV-10 keV) photons and electrons. The model is based on Monte Carlo simulations of the tracks and energy loss resulting from single electron scattering events with the constituent molecules of air, namely N2 and O2. The simulation code is based on the Geant4 toolkit. The original physics in Geant4 low-energy processes for photon interactions was used for the incoming photons and secondary X- and gamma-rays, from energies below 1-10 keV. Two new electron interaction processes were developed,and both of them were considered as discrete processes. The new implemented physics is based on experimental cross-sections for elastic and inelastic scattering, complemented with theoretical calculations. Ionization is treated as a subprocess of the inelastic process. The implementation of the new processes in the standard Geant4 frame is considered. Validation tests and comparison with other Monte Carlo results are discussed. The current limitations of this version of the code are also outlined. The code can be of interest in areas where energy deposition at microscopic level is crucial, such as microdosimetry.