The effect of the formation of vacancy lines on the kinetics of irradiation damage in graphite single crystals

Abstract

The concept of collapsed lines of vacancies formed by the random agglomeration of irradiation-produced point defects was introduced to explain certain observed irradiation properties of graphite. In the present paper this concept is examined theoretically in more detail and a kinetic irradiation damage model is developed. This model, besides accounting for the random formation of the vacancy complexes, makes allowance for the nucleation of interstitial clusters and their subsequent growth and for the annihilation of interstitials at vacancies. Analysis of the differential equations of the model gives estimates of the density of the various defects and, by making assumptions of the role played by these defects in producing the macroscopic properties, the model can be compared with observed experimental results. The model successfully predicts the concept of “break-away” as observed in the crystal growth data and, allowing for the inaccuracies inherent in the assumptions made and in the calculation of the various model parameters, the results predicted are in good agreement with the experimentally observed data on growth and total stored energy. The model also predicts the dynamic nucleation of the “hidden population” of interstitial defects.