Monte Carlo Simulation of Photon and Electron Transport in Matter

Abstract

Monte Carlo (MC) methods are a group of numerical techniques that have in common the use of stochastic algorithms to simulate the behaviour of mathematical or physical systems. They are based on the modelling of individual object-object relationships, which offers a large flexibility to tackle complex problems. The implementation of a MC solution to the problem at hand requires the random sampling of a large number of such object-object interactions to obtain the average value of some quantity of interest and its associated uncertainty. Radiation physics is a field where MC techniques are extensively used to model the propagation and interaction of ionizing radiation through matter. The focus of this chapter is the MC simulation of photons and light charged particles (electrons and positrons), excluding heavy charged particles (protons, alpha particles, etc.) as well as neutrons. The considered energies span from around 1 keV to 100 MeV. In spite of these restrictions, the selected types of ionizing radiations and energy interval allow to tackle many important applications in all areas of medical physics. The chapter summarizes the interaction processes experienced by photons and electrons. Random numbers, sampling methods, and the principles of multiple scattering of electrons are briefly addressed. Sections are devoted to the MC simulation of photon and electron transport and a description of available general-purpose MC codes. A simple example of MC simulation is also presented.