The annihilation characteristics of positrons in various types of diamond were studied by measuring 2-dimensional angular correlations of the positron annihilation Doppler broadening profiles and lifetime spectra. It was deduced from the measurements that there was a small number of defects in type-Ib synthesized diamond, and that the positron lifetime was 115ps. On other hand, it was found that positronium was formed in natural diamonds. The results of double X-ray measurements suggested that IIa-, IIb- and Ia-type natural diamonds could also contain empty space between the crystallites or grain boundaries.

S.Fujii, Y.Nishibayashi, S.Shikata, A.Uedono, S.Tanigawa: Journal of Applied Physics, 1995, 78[3], 1510-3