Energy Dependence of Electron Damage in Copper

Abstract

Electron irradiation below 1-Mev and subsequent recovery in copper have been investigated. The minimum threshold displacement energy is found to be less than 22 ev. The details of the recovery in stage I, as a function of electron energy, are found to be more complex than anticipated. Specifically, ${\mathrm{I}}_{a}$ decreases, ${\mathrm{I}}_{b}$ increases slowly, and ${\mathrm{I}}_{c}$ increases rapidly, respectively, in relative importance as the electron energy is reduced. A calculation of the cross section for displacement of copper atoms by electrons is also presented. A Born-Mayer potential with standard parameters is used. Only displacements in or near the close-packed directions are evaluated in detail. Other directions do not appear to contribute significantly in the near threshold energy region being considered. The agreement between this theory and experiment is found when a minimum threshold displacement energy between 19 and 20 ev and a Frenkel resistivity between 2 and 3 \ensuremath{\mu}ohm cm per atomic percent of interstitial-vacancy pairs is assumed.