DIFFUSION TRAPPING MODEL FOR POSITRONS TRAPPED AT RANDOMLY DISTRIBUTED THERMAL VACANCIES IN METAL

The paper presents the exact solution of the one-dimensional diffusion trapping model (DTM) for trapping of positrons at vacancies. The expl icit expressions are given for the positron lifetime spectrum and for the mean positron lifetime within this model, which were applied to th e description of the positron annihilation measurement with thermally generated vacancies. The values for the vacancy formation energy obtai ned from this model were equal to (0.51 +/- 0.005) eV for Pb and (0.48 +/- 0.016) eV for Cd. They are a bit smaller than those obtained for the standard positron trapping model and correspond well to the values obtained by other absolute methods.