FLUCTUATION EFFECT OF POINT-DEFECT REACTION ON NUCLEATION OF INTERSTITIAL CLUSTERS DURING NEUTRON-IRRADIATION

Effects of stochastic fluctuation of point defect reaction on the destination of small interstitial clusters were discussed. Nuclei of interstitial clusters are known to be formed directly from cascade collisions during neutron irradiation. However, the number of experimentally observed interstitial clusters is always much less than the number of cascade collisions in all the materials observed. Success fraction of interstitial cluster nuclei for growth was less than 1/10 in thin foil irradiated samples and less than 1/1000 in bulk irradiated samples, even in the atmosphere of excess free interstitials. These results cannot be explained by rate theory, and stochastic fluctuation of the absorption of free vacancies and interstitials is expected to be playing the major role. The repetition of the shrinkage and growth can make most of the small interstitial clusters produced by cascade collision shrink to zero size.