On the annihilation radiation of positrons

Abstract

The annihilation of positrons may occur either (1) when the positron is in motion, or (2) when it has already been stopped. In the first case, which will be discussed in this paper, either one or two quanta may be emitted. The two-quanta annihilation, which was first considered by Dirac, may occur between any free or bound electron and the positron, whereas only very tightly bound electrons can annihilate a positron with emission of one light quantum only. The annihilation of positrons which are already stopped takes place practically only with emission of two quanta. The one-quantum annihilation of slow positrons is extremely unlikely since the positron cannot get to the tightly bound electrons owing to its being repelled by the atomic field.