AGGREGATION OF FRENKEL DEFECTS UNDER IRRADIATION - A MESOSCOPIC APPROACH

The radiation-induced aggregation of Frenkel defects in solids is stud ied in terms of a mesoscopic approach. The asymmetry in elastic intera ctions between mobile interstitials (I-I) and between interstitials an d vacancies (I-V) plays a decisive role in the aggregation of similar defects. The conditions for defect aggregation are studied in detail f or NaCl crystals. The critical dose rate for aggregation has been calc ulated as a function of the temperature as well as the aggregation rat e as a function of 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 in terstitials, are studied. The aggregation appears to Teach a maximum a t a distinct temperature which is in agreement both with experiment an d the Jain-Lidiard theory. The model also predicts a shift of this max imum towards lower temperatures if the dose rate is decreased. The con sequences of the model for the disposal of nuclear waste in rock salt formations are briefly discussed.