Trapping model for thermal and nonthermal positrons in metals

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Abstract
In order to correct the discrepancies of the simple two-state trapping model currently being used to explain the temperature dependence of positron annihilatoin in metals, we have modified the standard trapping model to implicitly include nonthermal trapping of positrons in vacancies and divacancies. A positron-energy-loss function and energy-dependent trapping rates were used to calculate the mean lifetime and intensity of the trapped and untrapped positrons. We have fitted this model to the lifetimes for aluminum measured by Jackman et al. Results obtained for the formation enthalphy of vacancies and divacancies show the feasibility of the model to fit the experimental data.