Positrons in alkali halides

Proper symmetry wavefunctions for positrons in alkali halide crystals are calculated through a plane wave expansion. The band contributions to the effective masses are given. The anisotropies in the momentum distribution due to annihilations in the band states are examined, and the relative importance of anions and cations to annihilation events is assessed. The diffusion of positrons is discussed within a polaron picture, and some previously proposed models for the origin of the longer-lived lifetime component are dealt with.