Behavior of collision cascades at elevated temperatures in copper and molybdenum crystals

Self-ion irradiation was used to study the collapse of displacement cascades in pure copper, and molybdenum in the temperature range 200C to 5000C. In 30 keV self-ion irradiation of copper the number of vacancy loops formed from the cascades was observed to remain constant at temperatures below 3000C but to decrease sharply at temperatures above this. In 60 keV self-ion irradiation of molybdenum a gradual decrease in the number of vacancy loops was observed above 2000C, an order of magnitude decrease occurring by 5000C. The variation in numbers is compared with the predictions of a model which considers only thermal vacancy emission from the loops. This was found to give very good agreement for the copper results but not for the molybdenum results. Preliminary results are also reported on the effect of temperature on the Burgers vectors of the vacancy loops and on 60 keV self-ion irradiation of nickel