Non-uniform distribution of positron traps in plastically deformed aluminium

In an experimental study of positron annihilation in cold-worked aluminium, deviations from the simple trapping model are observed. It is shown that these deviations can be attributed to the non-uniform distribution of positron traps over distances larger than the positron diffusion length. TEM examinations support this hypothesis. According to a modified version of the trapping model, measured annihilation parameters are correlated to the volume fraction occupied by zones with very high positron trap density, and to the capture rate in the less damaged zones.