Distinguishing between radiation damage models by electron microscope studies of ion damage in metals

The paper reports on the use of transmission electron microscopy (TEM) for discriminating between the crowdion version of the two-interstitial model and other models of radiation damage. The method is based on the specific prediction of the crowdion model that, as a function of the irradiation temperature, vacancy clusters in heavy-ion-bombardment metals should show an increase in size within a narrow temperature interval around the temperature at which the metastable crowdions undergo thermal conversion into the stable Stage-III interstitial configuration. TEM of vacancy clusters produced by irradiation with 30 kV Cu+ ions shows such increases in Ni, Cu, Ag, and Pt, whereas the cluster sizes in Au are independent of the irradiation temperature. These results confirm the crowdion model for Ni, Cu, Ag, and Pt as well as the long-standing prediction that in Au the migration of crowdions is suppressed by thermal conversion. (In contrast to the other fcc metals, in Au the crowdion conversion enthalpy Hsub(C)sup(C) is smaller than the crowdion migration enthalpy Hsub(C)sup(M)). The estimates of Hsub(C)sup(C) and of the ranges of collision chains derived from the present data on Ni, Cu, Ag, and Pt are found to be in good agreement with other experiments. (author)