Stored Energy Measurements in Irradiated Copper

Thin copper foils, cooled to liquid nitrogen temperature, were subjected to bombardment by 12-Mev deuterons. The stored energy released due to annealing of the radiation damage was measured as the foils warmed to room temperature. Below -40°C the stored energy released per °C was approximately uniform and is presumed to result from annihilation of closely spaced interstitial-vacancy pairs produced by the bombardment. A prominent maximum in the annealing spectrum occured at -15°C and is interpreted as binary recombination of interstitial atoms and vacancies by means of interstitial diffusion. Changes in residual electrical resistivity were also measured. The stored energy to resistivity ratio was found to be 1.7±0.2 cal/gram per micro-ohm-cm, both for the low-temperature processes and the -15°C annealing peak. If the energy of formation of an interstitial-vacancy pair is 5 ev, a value of 11 micro-ohm-cm for the resistivity of one atomic percent of pairs is obtained. The atomic concentration of interstitial atoms and vacancies produced by an irradiation of ${10}^{17}$ deuterons/${\mathrm{cm}}^2$ at liquid nitrogen temperature is, accordingly, 5×${10}^{-5\mathrm{}}$.