The effects of vacancies on positron annihilation in cadmium

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Abstract
The strong temperature dependence of positron lifetimes in some metals has been explained in terms of the trapping of positrons by vacancies. To test the model further, precision measurements of the angular distribution of annihilation photons have been performed on samples of carefully annealed cadmium metal. The results, which are analysed in terms of the trapping model, provide a value of 0.52 ± 0.05 eV for the activation energy for vacancy formation in cadmium and emphasise the importance of core annihilation in the study of positron behaviour in metals.