Enhanced nucleation of radiation damage in graphite

Abstract

The homogeneous nucleation theory of radiation damage in graphite suggests that interstitial atoms collect into clusters on a scale dependent on the temperature of the graphite and the damage flux to which it is exposed. Experiments have been conducted involving short irradiations (6 hr-6 days) in a materials testing reactor at a lower temperature (~150, 200 or 350°C) followed by several months' irradiations at a higher temperature (350 or 650°C). The long term nucleation pattern has been shown by transmission electron microscopy to be profoundly modified by the short initial treatment, and the total rate of accumulation of interstitial atoms is considerably increased. The effects of the enhanced nucleation on macroscopic properties have been demonstrated by comparative measurements of dimensional changes and thermal resistivity increases during 350°C irradiation of specimens ‘seeded’ at 150°C.