Overview of physical interaction models for photon and electron transport used in Monte Carlo codes

The physical principles and approximations employed in Monte Carlo simulations of coupled electron–photon transport are reviewed. After a brief analysis of the assumptions underlying the trajectory picture used to generate random particle histories, we concentrate on the physics of the various interaction processes of photons and electrons. For each of these processes we describe the theoretical models and approximations that lead to the differential cross sections employed in general-purpose Monte Carlo codes. References to relevant publications and data resources are also provided.