Energy Transfer and Energy Absorption in Photon Interactions with Matter

Abstract

This chapter presents a discussion of the important mechanisms involved in energy transfer and energy absorption in an absorber irradiated with an external photon beam. The difference between energy transferred to charged particles in absorber and energy ultimately absorbed in the absorber is attributed to energy radiated from these charged particles in the form of photons. The mean radiation fraction and its three components (bremsstrahlung, in-flight annihilation, and impulse ionization) are defined and used to determine the total mean energy absorption fraction, as well as the mass energy absorption coefficient and the mean energy absorbed in the absorbing medium. The chapter concludes with two specific examples of photon beam interaction with an absorber (2 MeV photons with lead absorber and 8 MeV photons with copper absorber).