Abstract
We show that atomic-electron screening and subshell-ratio effects in single-quantum pair annihilation, reported by Broda and Johnson and by Sheth and Swamy, have a simple origin observed also in pair production and atomic photoelectric effect. In all three processes, the characteristic distances are small on an atomic scale, but large on a nuclear scale; wave functions have a point-Coulomb shape, but not the point-Coulomb normalization. Atomic-electron screening effects cause appreciable modifications of the total pair-annihilation cross section for positron energies below in heavy elements (). For low- elements, screening effects are always important. The rule of Bethe for subshell ratios is good only for low- elements (where is the prinicipal quantum number); we find that the subshell ratio between the and single-quantum pair-annihilation cross sections is well predicted by the square of the ratio of the and bound-electron wave-function normalizations.
- Received 20 November 1972
DOI:https://doi.org/10.1103/PhysRevA.7.1423
©1973 American Physical Society