Hydrogen and deuterium uptake in helium implanted layer of Mo and W

The accumulation of hydrogen isotopes in the helium (He) implanted layer of Mo and W single crystals was studied, focusing on the effects of the high dose irradiation of He ions and on uptake behavior of hydrogen (H) and deuterium (D) in various H2 and D2 pressure. A remarkable H uptake occurs in the He saturated layer of the crystals irradiated by 10 keV 4He ions to a dose about 2×1022 He/m2, after the heat treatment up to 850 K. The integrated amount of retained H reaches the same values before the thermal release procedure, though H-uptake rates depend on the gas pressure. The H is preferentially uptaken in the He saturated layer, when D2 and/or D2O gas is introduced in the vacuum chamber. The large difference between the H- and D-uptake rates suggest the oxide formation at the crystal surface where the microstructure is significantly changed due to the He irradiation.