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

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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