Annealing Studies of Irradiated Platinum

A field-ion microscope operated at 4.2^∘{}K has been used to study defects introduced into 99.9998% pure platinum by fast-neutron irradiation. Damaged or depleted zones have been identified and their concentration and size have been studied as a function of dose and annealing temperature. Direct observations indicate a distribution of zone sizes up to approximately 40 {} in diameter. The density of these zones is linear with dose in the range from 10¹⁶-10¹⁸ n/cm² ($E>1.45$ MeV). Field-ion-microscope studies also reveal that upon annealing through stage-IV recovery, the small depleted zones (15 {}) grow, causing an increase in the density of zones in the range between 15-30 {}. Simultaneously, the largest of the depleted zones present collapse to form dislocation loops lying on {110} planes. The remaining depleted zones are removed at temperatures corresponding to that of self-diffusion. Stage-III recovery in platinum has also been studied by examining specimens irradiated at temperatures above and below stage-III recovery. Direct observation indicates that some form of interstitial-atom motion must be associated with this recovery stage. The possibility of vacancies moving in this temperature range is specifically ruled out by energy considerations.