Neutron irradiation damage in molybdenum

Molybdenum single crystals (7000 ≤ ρ293°K/ρ4·2°K ≤ 8000) have been irradiated to a dose of ∼ 7 × 1019 fission n. cm−2 at 473°K and defect structures have been investigated by electron trasmission microscopy prior to and after a post-irradiation anneal of one hour at 1173°K. A quantitative and geometrical characterization has been carried out on small defect clusters (20 Å ≤ image diameter ≤ 100 Å) in an irradiated crystal and on resolved dislocation loops (100 ≤ image diameter ≤ 1100 Å) in an irradiated–annealed crystal. These two structural states have been related in terms of both the nature and the density of visible defects. The irradiated structure has also been compared in these terms with molybdenum crystals of the same purity damaged at 77°K to doses of ∼ 1 × 1020 and ∼ 5 × 1017 fission n. cm−2.