The nature of black-spot damage in irradiated gold

Abstract

High purity gold was irradiated with neutrons in a reactor and with high energy α-particles. The resulting black-spot damage was examined by electron microscopy. From stereomicrographs of foils decorated on one surface it was possible to measure the distance of certain defects from that surface. The direction of black-white streaking of the same defects was observed in the exact Bragg orientation. From this information the sign of the defects (whether they are of interstitial or of vacancy character) was deduced in each case. Foils about 1000 Å thick were α-irradiated at room temperature and the black-spot defects found to be of interstitial type. In the neutron irradiation case, bulk material was irradiated at about 65°C and the defects were found to have a vacancy character. In each case the symmetry of the black-white images was such that the defects are thought to be Frank loops. The result of the sign determination for the α-irradiation is in conflict with previous results. The discrepancy is believed to result from a previously unremarked denuded layer 40-50 Å deep at the surface.