Characters of defect clusters in irradiated metals

Character determinations for small point defect clusters have been made using depth measurements by stereo electron microscopy in conjunction with the observation of the senses of black-white images. In gold, nickel and aluminium bombarded with 80-150 kev heavy ions to doses ∼ 1015 m−2 and in neutron-irradiated gold the clusters were found to be of vacancies, confirming previous conclusions. For ion-bombarded metals character determinations by various workers fit a clear pattern. Vacancy clusters are formed from displacement cascades and may be observed by electron microscopy at doses ∼ 1015 m−2. However, if they are below the visibility limit, then ion doses ∼ 1019 m−2 give interstitial clusters by a diffusion mechanism. For neutron-irradiated metals results depend upon parameters that have not yet been sufficiently explored.