Evolution of radiation defects in nickel under low-temperature neutron irradiation

Neutron irradiation of pure nickel samples in an IBB-2M research reactor has been performed at a temperature of 305 K to damaging doses of 0.0015 and 0.15 dpa. Radiation defects formed in the material under irradiation have been investigated using transmission electron microscopy. It has been established that the main types of defects are vacancy clusters and interstitial dislocation loops. Sizes of vacancy clusters have been measured, and histograms of the cluster-size distribution have been constructed. It has been shown that, after irradiation with a dose of 0.15 dpa, the average cluster size is nearly half of that for samples irradiated with a dose of 0.0015 dpa. In the framework of the model of the migration of point defects, their evolution under irradiation has been analyzed. It has been shown that, at a temperature of 305 K, vacancies in nickel are immobile and migrating interstitials falling into clusters recombine with vacancies in them, which results in the exhaustion of clusters. The average life span of clusters has been calculated, and average concentrations of vacancies and interstitials under irradiation have been estimated.