Beyond the mean-field formulation of the production bias model

Abstract

The Production Bias Model was first conceptualized in the Silkeborg Workshop 10 years ago, to incorporate effects due to intracascade recombination, clustering and thermal dissociation of the clusters into the theory of microstructure evolution. Comparison of the theory with experimental results clearly supports the model, which has since been thoroughly reviewed. However, several important issues related to the probabilistic nature of cascade initiation and the statistical nature of the microstructure development have not received adequate attention. The most important feature of PBM is the production of damage in the form of point-defect clusters, both mobile and immobile, in cascades. Under most circumstances, the cluster population is one of the most important, if not dominant, components of the microstructure, the evolution of which controls the behaviour of the system under irradiation. Due to the small size of the point-defect clusters, fluctuations in the point-defect flux, caused by the stochastic nature of point-defect production and transport, govern their size distribution and number densities. Taking into account the effects of the fluctuating fluxes requires the formulation of PBM beyond the mean-field approximation. In this keynote paper, the readers are introduced to investigations in this vital area and the significance of the results obtained to the application of the production bias model in the analysis of microstructure development in solids during irradiation by neutrons and heavy ions.