Chapter 4 - THE ATTENUATION OF GAMMA RAYS

Abstract

The most important quantity characterizing the penetration and diffusion of gamma radiation in a medium is the linear attenuation coefficient. Its magnitude depends on the energy of the incident photon and on the atomic number of the material. There are three significant processes involved in the process of nuclear shielding, namely, the photoelectric effect, compton scattering, and electron–positron pair production. In atomic photoelectric effect, the incident photon disappears and an orbital electron is ejected from the atom. The electron carries away all the energy of the photon minus the binding energy of the electron in the atom. In compton scattering process, a photon collides with an atomic electron and loses some of its energy and is deflected from its original direction. It has an effect on the incident photon that is analogous to the effect that elastic scattering by an atomic nucleus has on a neutron―in both cases the incident particle survives the collision. In pair production effect, the incident photon disappears in the field of a charged particle and an electron–positron pair appears. The cross section for this process varies as the square of the charge of the target particle―which may be an atomic electron more usually, an atomic nucleus.