ANNEALING OF DEFECTS IN IRRADIATED NIOBIUM

Results obtained by means of positron annihilation for defect annealing in Nb irradiated by 7 MeV-electrons are present. The lifetime spectra for initial, irradiated and annealed samples were obtained using a standard ORTEC apparatus with time resolution 300 ps (FWHM). 22NaCl on mylar foil was used as a positron source. Analysis of theexperimental results allows concluding about the sample state after irradiation and the defect evolution during annealing. Monovacancies and interstitials trapped by impurities and some small vacancy clusters are present after irradiation. The interstitials release from impurities in the range 25-70°C, migrate and annihilate with monovacancies andvacancy clusters thus reducing the whole defect number without relative defect concentration changing (T2is constant, I2and K decrease). Releasing and migration of vacancies occur above 170°C (T2increases with microvoid size growth). © 1979 IOP Publishing Ltd.