Applicability of bremsstrahlung counting method to in-situ measurements of high level tritium.

为了建立热核聚变装置燃料循环中高水平氚的原位测量技术，研究了轫致辐射计数方法的适用性。对于轫致辐射计数方法的实际应用，需要允许在给定的材料表面上有效地产生轫致辐射x射线，并在材料中获得高透射率。从这个角度出发，我们通过理论分析研究了最适合轫致x射线产生和透过率的材料，并利用氚气对有前途的材料进行了测试。主要研究结果总结如下：采用硅雪崩光电二极管作为轫致辐射x射线探测器，该探测器具有体积小、易于维护等特点。从理论上评价了不同材料的轫致辐射x射线强度的变化。结果表明，铍是最理想的材料，对轫致辐射x射线的产生和透射率都比较充分。在此基础上，进行了氚气试验。结果表明，轫致辐射x射线的计数率与氚浓度成正比，检出限约为10^<-6>Ci/cm^3。也就是说，揭示了原位测量氚的量是可能的。另一方面，我们观察到计数率的下降是由于总压的增加引起的，即使氚的量保持不变。人们认为这种减少是由于射线在气相中的自吸收所致。在考虑自吸收的情况下，计算所得计数率在6%以内。因此，1)x射线探测器的小型化，2)探测效率的提高，3)寻找产生和透射韧致辐射x射线最有用的材料。结果表明，该计数方法对高含量氚的原位、实时测量是完全有效的。少

To establish techniques for in-situ measurements of high level tritium in fuel cycles of thermonuclear fusion devices, applicability of a bremsstrahlung counting method was examined. For practical use of the bremsstrahlung counting method, it is required to allow to generate efficiently bremsstrahlung x-rays on a given material surface and to gain high transmittance in a material. From this view point, we studied the most appropriate material to generation and transmittance of the bremsstrahlung x-rays by means of theoretical analyses, and the promising material was tested by using tritium gas. Summary of main results is as follows.1. A Si-avalanche photodiode was employed as a detector of the bremsstrahlung x-rays, which acts usefully at room temperature and has characteristics such as small size and easy maintenance. The variation of intensity of the bremsstrahlung x-rays was evaluated theoretically as to various materials. As a result, it was found that the beryllium is the best use … More full material for both of generation and transmittance of the bremsstrahlung x-rays.2. Based on this result, tests by tritium gas were performed. It was seen that the counting rate of the bremsstrahlung x-rays are proportional to tritium concentration, and the detection limit was about 10^<-6>Ci/cm^3. Namely, it was revealed that it is possible to measure in-situ the amount of tritium. On the other hand, it was observed that the decrease in the counting rate was caused by an increase in total pressure even though the amount of tritium is kept constant. It was considered that the decrease is due to the self-absorption of beta-rays in a gas phase. Taking into account of the self-absorption, the observed counting rate could be reproduced within 6% by computations.3. Consequently, 1) miniaturization of the x-ray detector, 2) enhancement of detection efficiency, 3) search of the most usefull material for generation and transmittance of the bremsstrahlung x-rays. 4) high sensitivity, and 5) analysis of the pressure dependence of the counting rate wee achieved, and it was concluded that the bremsstrahlung counting method is thoroughly valid for in-situ and real-time measurements of high level tritium. Less