Positron diffusion in solid and liquid Ga and Bi

The diffusion length of positrons in Ga and Bi was measured using a positron beam. For Ga, there is a drop from 1200(100) to 60(5) A upon melting; this is interpreted in terms of creation of centers that trap the positron. As the temperature of the liquid is increased, the diffusion length increases, suggesting that the size of the traps changes. For Bi, the diffusion length decreases from 500(30) to 190(10) A upon melting, and increases slightly as the temperature is increased. This drop is interpreted as increased positron-ion scattering, and not positron trapping as in Ga