Analog Electron Physics. Interaction Cross-Sections

The aim of the present communication is to describe briefly the physics of electron interactions in matter and its implementation in general-purpose Monte Carlo (MC) simulation codes. We shall limit ourselves to moderately high energies, say above 1 keV. At these energies, simulations can be performed on the basis of a trajectory model in which electrons are assumed to undergo discrete interactions with individual atoms (or molecules) of the medium. Between each pair of successive interactions, an electron moves freely, i.e. following a straight trajectory. The medium is considered as a dense isotropic gas, which implies that the length of each free flight is a random variable following the familiar exponential distribution. It is worth recalling that this simple picture overlooks coherent scattering effects (interference between waves scattered at different sites) which may become important at low energies, when the electron wavelength is of the order of the interatomic distances. In the energy range of interest here, the validity of the trajectory model can be justified by the same arguments that explain the production of cloud chamber tracks (see e.g. [1] p. 335). Within the trajectory model, all the information needed to simulate electron transport is contained in the atomic (or molecular) differential cross sections (DCS) for the various interaction mechanisms, namely, elastic scattering, inelastic scattering and bremsstrahlung emission. For a comprehensive tabulation of total (integrated) cross sections, see [2].