Recovery in neutron irradiated tungsten

The recovery of defects in partially and well annealed tungsten has been studied using electrical resistivity technique. The irradiation was carried out at reactor ambient temperature (∼343 K) to a fluence of 1022 n/m2. Isochronal annealing studies of the defects show two stages centred around 0.17Tm and 0.31Tm referred to as Stage III and Stage V respectively. Stage III shows a peak temperature shift to lower temperature for increasing amount of recovery. Isothermal annealing of the defects in Stage III and Stage V has been carried out and activation energy calculated using Meechan-Brinkman analysis. A single value of activation energy (1.69 ± 0.20 eV) and essentially a second order kinetics has been found in Stage III. However, no single value of activation energy could be obtained for Stage V (the activation energy varies from 2.5 to 3.6 eV). On the basis of the activation energy, reaction order and the negative shift in the peak temperature, Stage III has been attributed to arise due to migration of intrinsic point defects preferably self interstitials. It is difficult to attribute the changing activation energy in Stage V to a simple defect migration. However, it is possible that this observation could be explained on the basis of breaking of defect clusters.