THE RADIOLYSIS OF ALKALI-HALIDES - THE NUCLEATION AND GROWTH OF AGGREGATES

Since chemical reactions in the solid state are often complex, it is f requently difficult to analyse them quantitatively in terms of their u nderlying defect processes. This paper is concerned with one reaction - the radiolysis of alkali halides at moderately elevated temperatures - which, although complex, has proved amenable to detailed theoretica l analysis. More particularly, it is concerned with the formation and growth of aggregates of F-centres (''colloids'') created by the irradi ation of the crystal and with associated defect reactions. After an in troduction, section 2 reviews the underlying defect processes and the mechanism which leads to the creation of defect aggregates, especially aggregates of F-centres. Section 3 then describes the basic theory of the nucleation and growth of these aggregates. It also presents parti cular results pertaining to the nucleation stage and compares these pr edictions with (the rather limited) experimental data on nucleation. A much richer comparison of this kind is possible in the growth stage, where there is extensive data for F-centres and colloids in NaCl recor ded under irradiation as well as after irradiation. Section 4 makes a detailed comparison of this kind. This provides confirmation of the ki netic nature of the underlying processes, as well as of more particula r features of the model. Especially striking are the relaxation effect s accompanying sudden changes in radiation intensity (''dose-rate''). The theory of colloid growth provides a convincing interpretation of t hese (section 5). Conclusions and suggestions for further work are giv en in section 6.