Tracking of tritium trapped on/in high-Z materials by BIXS

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Trap and/or diffusion behavior of tritium in high-Z materials such as W and Mo, which are promising candidate as plasma-facing materials of fusion devices, have been studied by means of β-ray-induced X-ray spectrometry (BIXS). Main results obtained in the present study were as follows :(1) Diffusion behavior of tritium in W at room temperatureA given amount of tritium ions was implanted in a tungsten sample, and then change in β-ray-induced X-ray spectra at room temperature was tracked. The X-ray spectra observed were analyzed by means of computer simulation to estimate tritium depth profiles in tungsten. From change in the depth profiles, the diffusion coefficient of tritium at room temperature was estimated to be 2.4x10^<19> m^2/s.(2) Thermal behavior of tritium ions implanted into WThe tungsten sample irradiated with tritium was stepwise heated from room temperature to 700℃, and an X-ray spectrum was measured after each heating As a result, both X-ray intensities of Ar and W decreased with the increase of temperature, and they decreased to about 10% of the initial intensity at 500℃, indicating hat most of the implanted tritium desorbed from surface layers and bulk of the sample.(3) Effect of He pre-irradiation on the trap and diffusion behavior of tritiumWhen tritium was implanted into the He pre-irradiation sample, the X-ray intensity of Ar was about 5 times great in comparison with the He non-irradiation sample, and no change in the intensity at room temperature was observed for five months. Namely, it was seen that the retention of tritium strongly increased with the He pre-irradiation. The amount of tritium in surface layers decreased with heating, but that in bulk did not change up to 350℃. This indicates that the implanted tritium was strongly trapped at lattice imperfections formed by the He pre-irradiation, and the trapping energy of tritium was estimated to be about 1.2eV.