Fission fragment damage to metallic crystals

Abstract
Electron microscope observations of thin gold films irradiated with fission fragments have revealed the presence of small defect clusters. A comparison between the characteristics of their formation and growth at low doses and theoretical predictions indicates that these clusters are due to ‘depleted zones’, localized vacancy-rich regions created in situ by individual energetic primary or secondary knock-ons. Dark-field microscopy has shown that the majority of clusters are Frank loops (Burgers vector ⅓〈111〉), but a small fraction of perfect loops (Burgers vector ½〈110〉) is also found. Individual visible clusters contain between approximately 40 and 1100 vacancies. The implication of these results on the more general question of fission fragment damage in thin metal films is discussed.