Observation of small vacancy detect clusters produced by high- energy collision recoils

Abstract

The observation and analysis of small defect clusters produced by energetic particle irradiation is of importance in understanding the basic mechanisms of radiation damage. Renewed interest in fundamental studies stems from the need to understand very high energy recoil damage typical both of 14 MeV fusion neutrons and spallation neutrons produced around targets in high energy particle accelerators.The defect clusters may be of vacancy or interstitial type. Vacancy clusters occur -as vacancy loops, stacking fault tetrahedra, or three dimensional void embryos. Interstitial clusters occur as interstitial loops or three dimensional clusters. For irradiations carried out at temperatures below that which vacancies are predominantly immobile, analysis of the vacancy component of the total defect cluster population may be used to document the cascade collision processes produced by high energy recoils. The information required is defect cluster type, defect size distribution, and defect density. Since the defects of interest are generally in the size range 0.5 - 5 nm, electron microscopy imaging and analysis techniques are currently being re-assessed.