Defect clusters in neutron-irradiated vanadium containing oxygen

Single crystal samples of high-purity vanadium containing 95, 300, and 500 wt ppM oxygen were irradiated at 950C in the Ames Laboratory Research Reactor to a dose of 1.4 x 1019 neutrons/cm2 (E greater than MeV). The density and size distribution of radiation-produced defect clusters were analyzed by transmission electron microscopy in as-irradiated and post-irradiation-annealed material. The defect cluster density was observed to increase with increasing oxygen concentration and the average defect cluster size to decrease. Upon post-irradiation annealing the density decreased and the average size increased, but higher annealing temperatures were required for higher oxygen material. The results are discussed in terms of the nucleation of defect clusters at oxygen atoms and small oxygen-atom aggregates. The increased stability against annealing of higher oxygen vanadium is believed to be due to the greater segregation of oxygen at the defect clusters