An electron microscope study of radiation damage in single crystal graphite

Single crystals of graphite have been irradiated with neutrons to doses of up to 7·6 × 1019 n.v.t. (Ni) at temperatures up to 900°c and examined in the electron microscope. The damage is resolved on irradiation at temperatures of ∼250°c, and consists essentially of interstitial dislocation loops. Only a few per cent of the original number of point defects are collected into these loops. The crystals have been annealed after irradiation at temperatures up to 2200°c. The loops anneal out and there is evidence for their growth at high temperatures. It is concluded that the annealing out of the loops involves atom motion along the c axis and that the activation energy for this is ∼5·5 ev.