Helium and hydrogen trapping in W and Mo single-crystals irradiated by He ions

Retention of He and accumulation of H in the near surface layer of W and Mo single-crystals were studied during and after the implantation of He ions with 2-10 keV at 295 and 820 K. The He retention was saturated at a concentration of a He/metal ratio of about 0.25, depending on the implantation temperature. Subsequent He implantation caused H accumulation in the He saturated layer, up to a maximum concentration about equal to that of He. The initial H uptake rate just after the He irradiation was comparable to the impingement rate of the H-2 or H2O molecule at the crystal surface from the residual gas. For the He irradiation at 820 K, blisters and exfoliation with large sizes were observed on the crystal surface, where impurities other than H and He were also enriched. (C) 2002 Elsevier Science B.V. All rights reserved.