Single-quantum annihilation of positrons at low energies

Abstract

We discuss the low-energy single-quantum positron annihilation with a bound electron. The angular distribution and the total cross section are considered. We obtain a simple analytical expression for the Coulomb potential and for the screened potential. It is worth noting that the obtained results for the screened potential are universal and independent of the explicit form of the atomic potential. It is shown that screening significantly increases the cross section. We also obtain the analogous results for near-threshold bound-free e+e− photoproduction.