Enhancement effect on positron annihilation in solid argon and xenon

The life-time of a positron and the angular distribution of the resulting annihilation photons have been computed for solid argon and xenon using Chiba, Durr and Brandt formalism. In comparison to the earlier results obtained on Salvadori and Carbotte theory, the present calculation shows, both for Ar as well as Xe, narrowing of the angular distribution curve when the effects of electron-positron enhancement are included in the IPM results. Interestingly, for both Ar and Xe, the angular distributions computed from incoherent and coherent enhancement formulae look identical, but the total areas of the distribution curves come out to be different by a factor of about two in each case. The values of the mean-life for positron thus computed agree with the experiment only for the coherent case. (Auth.)