Residual gas-free specimens, and as-received specimens which were estimated to contain 4ppm of H atoms, were irradiated at 200C or 300C. The fluences ranged from 5.3 x 1018 to 1020/cm2. Stacking-fault tetrahedra and voids were observed. The number density of the voids decreased with increasing fluence, while the size of the voids increased with fluence. The voids formed uniformly in the specimens at low fluences, while some voids were observed near to dislocations at high fluences. The number density of stacking-fault tetrahedra increased with fluence at 200C. The number of vacancies which accumulated in a void was 350 times greater, than that in a stacking-fault tetrahedron, in specimens which had been irradiated to 5.3 x 1018/cm2 at 200C. At low fluences, the number density of voids was the same for as-received specimens and residual gas-free specimens. It was suggested that small vacancy clusters moved during irradiation, and that voids nucleated when the coalescence of small vacancy clusters occurred. The mobility of voids with gas atoms was lower than that without gas-atoms. This caused the number density of voids in as-received Cu to be greater than that in residual gas-free Cu.

Damage Evolution in Neutron-Irradiated Cu during Neutron Irradiation. I.Mukouda, Y.Shimomura: Journal of Nuclear Materials, 1999, 271-272, 230-5