First temperature stage evolution of irradiation-induced defects in tungsten studied by positron annihilation spectroscopy

The behaviour of vacancy like implantation-induced defects created in the track region of 800 keV 3He ions in polycrystalline tungsten was studied by Doppler broadening spectroscopy as a function of annealing temperature. A slow positron beam, coupled with a Doppler broadening spectrometer, was used to measure the low- and high-momentum annihilation fractions, S and W, respectively, as a function of positron energy in tungsten samples implanted at different fluences from 1014 to 5 × 1016 cm−2. The behaviour of the S(E), W(E) and S(W) plots with the annealing temperature clearly indicates that the irradiation-induced vacancy like defects begin to evolve between 523 and 573 K, whatever the implantation fluence. This first temperature stage evolution corresponds to the migration of the monovacancies created during implantation to form larger vacancy like defects of which depth profile is different from the initial radiation-induced defects one.