CRITICAL PARAMETERS CONTROLLING IRRADIATION SWELLING IN BERYLLIUM

Radiation effects in beryllium can hardly be explained within a framew ork of the conventional theory based on the bias concept due to elasti c interaction difference (EID) between vacancies and self-interstitial atoms (SIAs) since beryllium belongs to hexagonal close-packed metals where diffusion has been shown to be anisotropic. Diffusional anisotr opy difference (DAD) between point defects changes the cavity bias for their absorption and leads to dependence of the dislocation bias on t he distribution of dislocations over crystallographic directions. On t he other hand, the elastic interaction between point defects and cavit ies gives rise to the size and gas pressure dependencies of the cavity bias, resulting in new critical quantities for bubble-void transition effects at low temperature irradiation. In the present paper, we deve lop the concept of the critical parameters controlling irradiation swe lling with account of both DAD and EID, and take care of thermal effec ts as well since they are of major importance for beryllium which has an anomalously low self-diffusion activation energy. Experimental data on beryllium swelling are analyzed on the basis of the present theory .