Isothermal Annealing below 60°K of Deuteron Irradiated Noble Metals

Foils of 99.999% pure copper, 99.999% pure silver, and a copper alloy containing 3.78 atomic percent nickel were irradiated near liquid helium temperature with 10.7-Mev deuterons. Annealing up to 60°K was performed in a series of isothermal steps. During each anneal the decrease of the radiation-induced resistivity increment with time was observed. Resistivity distribution curves, obtained by assuming that recovery processes with a continuum of activation energies are present, show several small peaks followed by a large peak. The maxima occur at 0.048, 0.080, 0.091, and 0.113 ev in copper and at 0.045, 0.058, and 0.079 ev in silver. The frequency factors for both metals were found to lie between 7.2×${10}^{10}$ and 3.9×${10}^{12}$ ${\sec }^{-1\mathrm{}}$. Alloying served to broaden the energy distribution of the recovery processes. Changes in the Debye characteristic temperature of -(15±1)°K and -(10±1)°K were also observed in copper and silver, respectively. Annealing of these changes was about 80% complete at 50°K. The dominant mechanism in the low-temperature recovery is believed to be the annihilation of Frenkel pairs, with the interstitials as the mobile defects. A trapping model is proposed to explain why all the resistivity increment does not anneal out once interstitials begin to move.