Neutron irradiated tungsten bulk defect characterization by positron annihilation spectroscopy

Positron annihilation spectroscopy was used to evaluate the defects in neutron irradiated tungsten exposed at five different irradiation conditions. The variables in neutron irradiation included temperature, displacements per atom (dpa), and neutron spectrum. A set of W, Re, WRe, and WReOs control samples were used in assessing the data. Positron annihilation lifetime spectroscopy and coincidence Doppler broadening measurements revealed that samples irradiated at 500 °C had more vacancy clusters than samples irradiated at higher temperatures. This trend was observed despite some higher temperature samples having a significantly higher dpa. Positron lifetimes indicate these are divided into large (>40) and small (<10) vacancy clusters, respectively. These combined results elucidate the competition between defect production and recovery in plasma facing components, where at the irradiation conditions herein, temperature has a much stronger effect on defect size than does dpa.