Development of ionization chamber applying to in-situ measurements of high level tritium.

为了建立原位和实时测量高水平氚的技术，我们检查了电离室的适用性。为此，我们制作了一个有效体积为1.9 cm~3的小型电离室，并测试了其饱和电流曲线、氚浓度和总气压对电离电流的依赖关系等基本特性。一个小型电离室，内电极加到外电极上，由商业配件制成，易于与氚处理系统连接，即使在装载约3Ci氚的情况下也没有观察到电离室泄漏。在给定量氚的情况下，在20V以上的电势下，获得了良好的电离电流饱和特性。此外，当总气压保持在760Torr时，电离电流与氚浓度在1×10~(-6)~3×10~(-6)~3×10~(-1)~(-1)Ci/cm~3之间呈良好的线性关系。另一方面，对于总压力的变化，尽管每次运行的氚含量相同，但电离电流随着压力的增加而显著降低。这一变化主要是由于利林气体对射线的阻挡能力降低所致。然而，考虑到气相中的能量消耗随着压力的变化而降低，这种电离电流与压力的关系可以重现。这些结果表明，小型电离室的性能可以满足氚储存系统中高水平氚的在线和实时测量以及热核聚变装置燃料处理的要求。

To establish techniques for in-situ and real-time measurements of the high level tritium, we examined the applicability of ionization chamber. For this purpose, we fabricated a small ionization chamber whose effective volume was 1.9 cm^3, and examined the performances concerning with the fundamental characteristics such as saturation-current curve, dependences of tritium concentration and total pressure for the ionization current. A small ionization chamber that inner electrode was incorporated into outer electrode made of commercial fittings was ease in attachment to the tritium handling systems, and no leakage from the chamber was observed even the case of loading with about 3 Ci tritium. As a given amount of tritium was introduced into the chamber, a favorable saturation characteristic of ionization current was obtained by applying the potenial over 20 V. In addition, it was shown that the ionization current was quite well proportional to the tritium concentration in the range from 1x10^<-6> to 3x10^<-1> Ci/cm^3 when the total pressure was kept constant at 760 Torr. For the variation of total pressure, on the other hand, the ionization current decreased greately with the pressure even though the amount of tritium in the chamber was same in each run. This bhange was mainly caused by the decrease in the stopping power of lilling gas for -rays. Such pressure dependence of ionization current, however, could be reproduced by taking account of the decrease in energy consumption in gas phase with the pressure change. From these results, it was concluded that the performances of small ionization chamber were acceptable for the requirements on in-situ and real-time measurements of high level tritium in the tritium hadling systems as well as the fuel processing in thermonuclear fusion devices.