The Penetration of Gamma-Rays through Matter and the Development of Radiation Theory

Abstract

The absorption of γ-rays in passing through matter has played an important historical role in the development of relativistic quantum mechanics and quantum electrodynamics. This role was played more than once. As we shall see at the end of this article it may be that its function in this respect is not exhausted yet. It is possible that the Compton effect at extremely high energies may once more be invoked as a critical test — or as a guidance — for the last phase of development of quantum electrodynamics, which seems as yet to lie in a somewhat hazy future. The absorption of γ-rays is chiefly due to 3 causes. (I) The photoelectric effect, (II) Compton scattering, (III) pair creation. We may disregard the photo-effect which contributes strongly to the absorption only in the non-relativistic region ħv/mc ² ≪ 1, and this region is not so interesting for our discussion. In addition there is also selective absorption by nuclei but this we will not consider either.