Interaction of Radiation with Matter

Abstract

The term high-energy radiation is applied both to particles moving with high velocity—fast electrons or β-particles, fast protons, neutrons, α-particles, and charged particles of higher mass—and to electromagnetic radiation of short wavelength—X-rays and γ-rays. The processes by which these different forms of radiation react with the atoms of a specimen through which they pass may be different, the common feature being the large amount of energy carried by each particle or photon (this energy is very much greater than that binding any orbital electron to an atomic nucleus or an atom to its neighbor). In this respect, they differ from slow or thermal neutrons and from ultraviolet light, in which the energy carried per particle or photon is usually smaller than the ionizing energy of an atom or molecule. The effects produced by γ-rays or X-rays may be best understood as due to discrete high-energy photons, which may therefore also be considered as particles in this context. In most cases, the changes produced by incident radiation depend mainly on the total energy absorbed and very little on the type of radiation or its energy.