Doppler-broadening positron-annihilation measurements combined with electrical-resistivity measurements were performed on Cu and Al samples, irradiated by high-energy electrons at liquid-helium temperature. A defect-specific parameter R was determined from the shape of the 511-keV annihilation line. The R parameter is found to be independent of the defect concentration C and the positron trapping constant within the framework of the two-state trapping model. During isochronal annealing of electron-irradiated copper the line-shape parameter Iv increases in stage III, whereas the electrical resistivity decreases, indicating a reduction in the Frenkel-defect concentration. These two combined effects and the pronounced steps in the R parameter during stage-III annealing, which are found to be dose independent, signify that radiation-produced vacancies become mobile and coalesce into clusters before they anneal out. The positron trapping constant for vacancies in Cu was determined to be =(4.25×0.8)×1014 sec-1. Furthermore, the annealing behavior of copper and aluminum samples, deformed plastically at 77 K and irradiated at 4.2 K by electrons, respectively, is discussed. In both cases no indication for the formation of vacancy agglomerates is found during annealing. The R-parameter analysis is also applied to the data for electron-irradiated Mo, as reported by Eldrup et al. © 1978 The American Physical Society.    «

Doppler-broadening positron-annihilation measurements combined with electrical-resistivity measurements were performed on Cu and Al samples, irradiated by high-energy electrons at liquid-helium temperature. A defect-specific parameter R was determined from the shape of the 511-keV annihilation line. The R parameter is found to be independent of the defect concentration C and the positron trapping constant within the framework of the two-state trapping model. During isochronal annealing of electr...    »