Permeation of hydrogen through vanadium under helium ion irradiation

Hydrogen permeation through vanadium was examined under helium ion irradiation. The upstream surface of a vanadium membrane was exposed to hydrogen gas at 673 K and 640 Pa, and the downstream surface was irradiated with 5 keV helium ions. No significant variation in the permeation rate was observed in the initial stage of irradiation. The permeation rate, however, started to decrease at a helium ion dose of 1021 m−2 with further irradiation. In this region, the permeation rate dropped immediately by intermission of irradiation and shot up by resumption. These results were successfully explained with a model that helium bubbles act as trapping sites of hydrogen and detrapping is enhanced under irradiation.