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

利用β射线感生X射线能谱（BIXS）研究了氚在聚变装置等离子体面材W和Mo等高Z材料中的俘获和扩散行为。（1）室温下氚在钨中的扩散行为将一定量的氚离子注入到钨样品中，跟踪了室温下β射线感生X射线谱的变化。通过计算机模拟分析了所观察到的X射线谱，以估计氚在钨中的深度分布。根据深度剖面的变化，室温下氚的扩散系数估计为2.4x10^<19>m^2/s。(2)氚离子注入钨的热行为将氚辐照的钨样品从室温逐步加热到700℃，测量了每次加热后的X射线能谱。结果表明，随着温度的升高，Ar和W的X射线强度均下降，在500℃时下降到初始强度的10%左右。表明大部分注入的氚从样品的表面层和本体解吸。(3)He预辐照对氚俘获和扩散行为的影响He预辐照样品中注入氚后，Ar的X射线强度约为未辐照样品的5倍，室温下5个月强度无变化。也就是说，可以看出，氚的保留强烈增加与He预照射。在350℃以下，表层氚含量随温度升高而减少，而体相氚含量基本不变。这表明注入的氚被强烈地捕获在由He预辐照形成的晶格缺陷处，并且氚的捕获能量估计为约1.2eV。

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.