DEFECT ACCUMULATION UNDER CASCADE DAMAGE CONDITIONS

There is now ample evidence from both experimental and computer simulation studies that in displacement cascades not only intense recombination takes place but also efficient clustering of both self-interstitial atoms (SIAs) and vacancies. The size distributions of the two types of defects produced in cascades are not only different but this difference is also temperature dependent because of the different thermal stabilities of SIA and vacancy clusters. This asymmetry in the production of SIAs and vacancies has been termed ''production bias''. In the present paper, the basic physics of the defect reactions kinetics associated with the specific features of cascade damage is described, with emphasis on asymmetries between SIA and vacancy type defects concerning their production, stability, mobility and interactions with other defects. Defect accumulation under cascade damage conditions is discussed in terms of this reaction kinetics taking into account cluster production, dissociation, migration and annihilation at extended sinks. Microstructural features which are characteristic of cascade damage and cannot be explained in terms of the conventional single defect reaction kinetics are emphasized, in particular the heterogeneous microstructural evolution at low doses and the dose and temperature dependence of swelling.