Photon Interactions with Matter

Abstract

The radiation-matter interactions of interest to nuclear medicine are those\rof photons (X or g rays) and of charged particles (a particles and electrons). This\rchapter reviews the photon–matter interaction classes of interest to nuclear medicine\rdosimetry and classifies them in terms of whether or not the incident photon is\rpreserved through the process. In practice, this will be those major interactions that\roccur at photon energies below 1 MeV. The cross sections for Thomson and Rayleigh\rscatter, which are classical in nature, are derived; insignificant energy transfer results\rfrom such scatters although they do lead to attenuation of a photon beam. Compton\rscatter is reviewed extensively, including through the derivation of the Klein–\rNishina cross sections using the Feynman propagator method. Photoelectric absorption\ris next examined and the cross sections for photon absorption on the K-shell\relectrons derived. The excited atom must relax through either radiative or nonradiative\rmeans and these are reviewed and characteristic X-rays and Auger/Coster–\rKronig electrons introduced. Finally, the interaction coefficients used in dosimetry\rto describe photon–matter interactions are introduced.