A MESOSCOPIC APPROACH TO RADIATION-INDUCED DEFECT AGGREGATION IN ALKALI-HALIDES STIMULATED BY THE ELASTIC INTERACTION OF MOBILE FRENKEL DEFECTS

The radiation-induced aggregation of Frenkel defects in alkali halides is studied in terms of a mesoscopic approach. The asymmetry in elasti c interactions between mobile interstitials (I-I) and between intersti tials and vacancies (I-V) is shown to play a decisive role in the aggr egation of similar defects. Results obtained with a clear-cut approxim ation of the elastic interaction are compared with those obtained with a more correct long-range (r-3) potential. The conditions for defect aggregation are studied in detail for NaCl crystals. The critical irra diation intensity (dose rate) for aggregation is calculated as a funct ion of the temperature as well as the aggregation rate as a function o f temperature and dose rate. Furthermore, the role of deep traps (like impurities and di-vacancies), reducing the mobility of interstitials, and the role of dislocations serving as sinks for interstitials are s tudied. Aggregation appears to reach a maximum at a distinct temperatu re which is in agreement both with experiment and the Jain-Lidiard the ory. The model predicts a shift of this maximum towards lower temperat ures if the dose rate is decreased.