A theory was presented for the prediction of the momentum distributions of annihilating positron-electron pairs in solids. In order to test the theory, momentum distributions were deduced from the Doppler broadening of annihilation radiation for several bulk metals and semiconductors, semiconductor alloys and for positrons which were trapped at vacancies in semiconductors. The theory was based upon a 2-particle description of the annihilating electron-positron pair. It was found that electron-positron correlation effects (such as enhancement of the electron density at the positron) depended upon the electronic state in question. The theory was suitable for calculating the high-momentum part of the annihilation spectrum that arose from the core electrons and which could be deduced from the Doppler broadening by using coincidence techniques. The assumptions of the theory were supported by the good agreement between theory and experiment in the case of positron annihilation in defect-free bulk lattices. A comparison of the theoretical and experimental spectra for alloys and vacancy defects provided a theoretical description of the positron distributions in delocalized and localized states.

M.Alatalo, B.Barbiellini, M.Hakala, H.Kauppinen, T.Korhonen, M.J.Puska, K.Saarinen, P.Hautojärvi, R.M.Nieminen: Physical Review B, 1996, 54[4], 2397-409