Helium behaviour and vacancy defect distribution in helium implanted tungsten

The distribution and the nature of 3He implantation-induced defects in polycrystalline tungsten samples were studied by Positron Annihilation Spectroscopy as a function of implantation fluence. The implanted helium profile was determined by Nuclear Reaction Analysis, and its evolution under different thermal annealings was investigated. Results show that vacancy-like defects are generated along the path of the ions and that their concentration varies directly as the implantation fluence. No helium desorption was observed under any thermal treatments. However, a change in 3He depth profile under specific annealing conditions suggests the formation of nanometric-size He bubbles. © 2007 Elsevier B.V. All rights reserved.