A variable-energy positron beam was used to study this material. Differences in the line-shape parameter, between annealed and unannealed samples were observed. A diffusion-model analysis of the results revealed large changes in the bulk defect concentration, due to annealing.

C.Smith, P.Rice-Evans, N.Shaw, D.L.Smith: Materials Science Forum, 1992, 105-110, 1443-6