Positron annihilation experiments on electrons and neutrons of irradiated copper and aluminium

Doppler broadening measurements of the 511 keV annihilation radiation of the positron-electron pair were performed on copper and aluminium samples irradiated at low temperatures and on gold samples quenched during isochronal annealing. From the shape of the Doppler broadening curve a defect specific parameter R was determined. The information deduced from the R-parameter and the similar annealing behavior of electron-irradiated copper and quenched gold, leads to the conclusion that in Cu and Au the vacancies become mobile during annealing stage III and coagulate to small clusters. Electron irradiated aluminium does not show any formation of vacancy agglomerates during annealing stage III. In addition, the temperature dependence of positron trapping for different types of defects was studied. For single vacancies, produced by electron irradiation at low temperatures in aluminium, copper and nickel, positron trapping is temperature independent. However, a marked temperature dependence is observed for small vacancy clusters in copper, produced by electron irradiation and subsequent annealing, for dislocation loops in neutron irradiated copper and for voids in neutron irradiated aluminium. (orig.)