Anisotropy of the Threshold Energy for Production of Frenkel Pairs in Copper and Platinum

Thin copper and platinum single-crystal foils have been irradiated at liquid-helium temperature with electrons of energies between 1 and 3 MeV. From resistivity measurements the directional dependence of the damage rate was determined with high accuracy by varying the orientation of the foils relative to the direction of the beam of the irradiation electrons. From the dependence of defect production on electron energy and foil orientation, the angular dependence of the threshold displacement energy could be determined. In both fcc metals, the closest-packed directions $〈100〉$ and $〈100〉$ possess ring-shaped regions which show minimum threshold values down to 19 eV for copper and 33 eV for platinum, while maximum threshold values are attained near the $〈111〉$ direction. For the electrical resistivity per unit concentration of Frenkel pairs, we obtained (1.7 \ifmmode\pm\else\textpm\fi{} 0.3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ \ensuremath{\mu}\ensuremath{\Omega} cm for copper and (9.5 \ifmmode\pm\else\textpm\fi{} 0.5) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ \ensuremath{\mu}\ensuremath{\Omega} cm for platinum. For copper a comparison with other theoretical and experimental works is possible and shows satisfactory accordance.