Exposure time and recoil energy dependence of defect accumulation

Abstract

Experimental information frorn irradiations with a wide variety of energetic particles, electrons, ions and fission and fusion neutrons, is combined and analyzed to elucidate the mechanism of microstructure evolution during irradiation, with particular interest placed on the case of cascade damage. A brief survey of the case of homogeneous introduction of point defects, electron irradiation with high voltage electron microscopes, is made. Stochastic fluctuation of point defect reaction and positional instability of shall point defect clusters are among new subjects. A kinetics analysis is made for each of the categorized cases of time evolution of defect structures during irradiation with cascade damage. The cases analyzed include vacancy cluster accumulation from cascades by the impact effect from cascades (proportional to the square of irradiation dose), and the extent of impact influence from cascade collisions is estimated. Vacancy cluster accumulation from cascades with efficient permanent sinks (proportional to irradiation dose) and with poor permanent sinks (proportional to the square-root of irradiation dose). The case with interstitial cluster formation (proportional but with smaller accumulation rate) is treated separately from the case without. For the nucleation of interstitial clusters from cascades, the important role of the fluctuation of point defect reactions to suppress the nucleation is emphasized. The influence of the positional instability of small interstitial clusters plays a role in interstitial type defect structures. Finally, a method is proposed to improve the currently poor situation of fission-reactor neutron irradiation into a systematic and reliable experiment.