Positron-annihilation study of silver irradiated by energetic protons or neutrons

To study the relationship of recoil energy to damage production we have irradiated well-annealed samples of silver at room temperature with energetic protons from 4.5 to 22.5 MeV or D-T fusion neutrons up to maximum fluences of $6\times {10}^{17}p{\mathrm{cm}}^{-2\mathrm{}} \mathrm{and} \times {10}^{17}n{\mathrm{cm}}^2$. Positron-annihilation analysis including both lifetime and Doppler-broadening profile data was used to determine the characteristics of the surviving defects. The trapping-rate data exhibit a strong nonlinear fluence dependence, which may be due to radiation annealing of the damage. There is also clear evidence of a threshold recoil energy below which the defect survival efficiency is very low. This threshold is determined to be between 50- and 100-keV recoil energy.