Abstract
The authors propose a novel formalism to calculate the positron annihilation characteristics in solids in which the positron-electron product (PEP) wavefunction is obtained directly from a wave equation. From this PEP equation it is easy to see that the most structure-dependent term, the Coulomb potential, present in the individual electron and positron wave equations is cancelled exactly. The remaining potential is a considerably smoother and weaker function than the Coulomb potential. In a qualitative analysis, one can then easily explain some typical but apparently paradoxical features in earlier treatments. As an illustration of the PEP formalism the authors have calculated the bulk angular correlation distribution of a positron annihilating in Al metal. Within the new formalism the effect of the crystalline potential (symmetry) and of the many-body interaction on the angular correlation distribution can be calculated in a phenomenological way. The results are in good agreement with experiments, even as regards the finer details, and compare well with the conventional formalism. The advantages and shortcoming of the new formalism are discussed.
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