Behaviour of positrons in low melting metals investigated by life-time measurement

We have measured positron lifetimes in polycrystalline samples of Cadmium, Indium, and Tin in the whole temperature range from 80 K to the respective melting points. In all three metals we found clear deviations of the behaviour of positrons from that predicted by simple trapping-models. The additional effects are properly explained by depletion of shallow traps in the lowest temperature region and by trasient dilatation-trapping in the prevacancy region. The formation-enthalpy of monovacancies can be determined from the trapping effect by the use of a 'threshold-temperature'. We obtain Hsup(f)sub(v)=0.46 eV in Cd, 0.44 eV in In, and 0.58 eV in Sn. As a special result we succeeded in detecting the transition from the β- to the α-phase of tin by a method of the positron-annihilation-technique for the first time. (Author)