High Concentration Tritium Gas Measurement with Small Volume Ionization Chambers for Fusion Fuel Gas Monitors

Abstract

To apply ionization chambers to fusion fuel gas processing systems, high concentration tritium gas was experimentally measured with small volume 0.16 and 21.6 cm3 ionization chambers. From plateau curves, the optimum electric field strength was obtained as 100–200 V/cm. Detection efficiency was confirmed as dependent on the ionization ability of the filled gas, and moreover on its stopping power, because when the range of the β-rays was shortened, the probability of energy loss by collisions with the electrode and chamber wall increased. Loss of ions by recombination was prevented by using a small volume ionization chamber. For example the 0.16 cm3 ionization chamber gave measurements with linearity to above 40% tritium gas. After the tritium gas measurements, the concentration levels inside the chamber were estimated from their memory currents. Although more than 1/4,000 of the maximum current was observed as a memory effect, the smaller ionization chamber gave a smaller memory effect.