A positron annihilation study of defect recovery in electron-irradiated ?-Zr

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Abstract
The presence of vacancy defects in α-Zr, irradiated at 320 > T > 290 K with 1.5 MeV electrons, has been indicated by positron annihilation measurements. It was found that positron lifetimes associated with annihilation in well-annealed α-Zr, fell in the range 173 to 181 psec, with no obvious dependence on the sample purity or grain size (down to 10 microns). After irradiation, however, the mean lifetime increase-associated with defect trapping-was found to be bigger for lower purity Zr, a result that was emphasized in a multicomponent analysis. Isochronal annealing studies on the less pure Zr showed nearly continuous recovery up to 550 K, while other specimens exhibited no measurable recovery below 450 K. Potential effects of particular impurities are considered in terms of their interstitial/substitutional nature, inferred from tracer diffusion studies.