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

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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.