A comparison of initial damage rates due to electron and neutron irradiations measured by internal friction techniques. III. Neutron energy dependence (67 keV to 1 MeV)

摘要

Neutron energy dependence of the initial dislocation pinning rate was studied from 67 keV to 1 MeV on a copper sample. By comparing the initial pinning rates of 0.5‐MeV electron irradiations and the neutron irradiations and using the defect production rate for electron bombardments, an estimate of the free interstitial production cross sections for neutrons was made. Comparison with the Norgett‐Robinson‐Torrens production cross section for the total number of defects was made to estimate the fraction of defects surviving as free interstitials. Previous data covering the neutron energy range of 2–24 MeV showed this fraction to be a constant. However, the present lower energy data show that the survival fraction increases at low energies, from 0.7% at 1 MeV to 2% at 67 keV. The entire data set is compared with two additional models, one which considers experimental data and computer models supporting a recoil energy dependent displacement efficiency and one which yields the number of free vacancies after short‐term annealing. Our results are best described by the latter. It is concluded that the surviving fraction of defects in displacement cascades is a function of primary knock‐on energy in the few keV range and that this behavior must be considered in modeling radiation effects.