Positron-lifetime study of secondary-defect formation in quenched aluminum

Positron-annihilation lifetime measurements were made on quenched aluminum as a function of isochronal annealing in the (130--450)-K temperature range. Secondary-defect formation was detected at 210 K. The appearance of a separate long-lifetime component in the lifetime spectra above 280 K showed the presence of small three-dimensional vacancy clusters in the samples. The annealing of vacancy clusters results in the formation of dislocation loops showing strong temperature-dependent trapping of positrons. These defects are interpreted as shallow traps for positrons.