The mean positron lifetime, positron diffusion length and the positron and electron work functions for polycrystalline material were experimentally determined. It was deduced that the mean positron lifetime was 160ps, that the positron diffusion length was 138nm and that the electron work function was 1.96eV. The positron work function was probably positive. The results strongly supported the suggestion, based upon first-principles electronic structure and positron state calculations, that positrons were trapped by, and annihilated in, metal vacancies. The results of XPS measurements indicated that the trapping sites were located mainly in thin C-rich layers between grains. This was also thought to explain the large near-surface diffusion length.

G.Brauer, W.Anwand, E.M.Nicht, P.G.Coleman, A.P.Knights, H.Schut, G.Kögel, N.Wagner: Journal of Physics - Condensed Matter, 1995, 7[47], 9091-9