Kuniaki Watanabe, Kan Ashida, Kenji Ichimura

Tritium Research Center, Toyama University, 3190 Gofuku, Toyama 930, Japan

Abstract

    Trapped states of deuterium implanted into a pyroytic graphite with 5 keV investigated by means of X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). Chemical shift of the C1s peak was observed in the XPS spectra due to the deuterium implantation at room temperature. The shift increased with the deuterium fluence to reach a constant value (0.4 eV). In the SIMS spectra, CD^- and C₂D^- peaks arised due to the implantation. The relative intensity of the former increased with the fluence to reach a constant value, whereas that of the latter passed through a maximum to decrease to a constant value. A linear relation was observed between the chemical shift and the relative intensity of the CD^- peak. The chemical shift and theCD^- peak disappeared by annealing the sample at 600℃, whereas the C₂D^- peak disappeared at 900℃.
    On the basis of these observations, it is concluded that the deuterium is trapped in/on the graphite in two different states: one is C-D (on-top form) and the another is C₂-D (bridge form) species.

K. Ashida, K. Ichimura, M. Matsuyama, H. Miyake, K. Watanabe

Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    Chemical sputtering of graphite and the retention of hydrogen are important subjects for thermonuclear fusion devices. We measured thermal desorption processes of deuterium implanted into graphite at room temperature by means of the flash desorption spectroscopy along with surface characterization by XPS and SIMS. Chemical shift of the C1s peak was observed by XPS due to the deuterium-ion implantation. In SIMS spectra, CDx^± and C₂D^- signals appeared after the implantation. Based on these observations, it was concluded that C-D and/or C₂-D species were formed on the surface due to the implantation. The implanted deuterium desorbed as D₂ and CD₄ by flashing the sample above 500℃. The fraction of the desorbed amount of CD₄ strongly depended on the flashing mode. Moreover, no methane appeared after the irradiated sample was annealed above 500℃. It was concluded that a part of the C-D and/or C₂-D species associated each other in the graphite during the flash desorption to form molecular deuterium which presumably adsorbed on carbon atoms.

Masao Matsuyama, Hitoshi Miyake, Kan Ashida, Kuniaki Watanabe

Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan

Abstract

    Tetrafluoroethylene (TFE) is widely used for conventional tritium handling systems such as vacuum seals, tubing and so on. We measured the permeation of the three hydrogen, methane and the inert gases through a TFE film at room temperature by means of the time-lag method in order to establish the physicochemical properties which determine the solubility and diffusivity of those gases. It was found that the diffusion constant of the inert gases changed exponentially with the heat of vaporization and the solubility was an exponential function of the Lennard-Jones force constant of the gases. On the other hand, hydrogen isotopes and methane deviated from these relations. It is concluded that chemical interactions between the solute and the solvent play an important role for the dissolution and the diffusion of these gases in TFE.