Theoretical foundation and extension of the trapping model

The trapping model frequently used for analyzing experiments on positron annihilation in solids is put on a firm theoretical basis by deriving it from Waite's theory of diffusion-limited reactions. The conventional version of the trapping model turns out to be correct only if the trapping process is not diffusion-limited and if the escape probability of positrons from traps is negligibly small. The present paper treats both detrapping and the effects of positron diffusion for an arbitrary number of different types of traps, and develops a perturbation-theory solution for the general case.