A SMALL IONIZATION-CHAMBER APPROPRIATE TO TRITIUM PROCESSING SYSTEMS

Small sized ionization chambers are attractive as a continuous tritium flow monitor in the fuel processing systems. We made a small ionization chamber and examined some basic properties of it such as saturation-current characteristics, concentration and/or pressure dependence of the ionization current, and impurity gas effects. A small ionization chamber of 1.9 cm3 in volume showed satisfactory saturation-current characteristics above 20 V, and also gave a good linear relationship between ionization current and tritium concentration in a wide range from 1 x 10(-6) to 3 x 10(-1) Ci/cm3 under condition of 1 atm. The pressure dependence of the ionization current was analyzed through a simple two-dimensional model taking account of the energy consumption of beta particles in the chamber. Addition of inert gases to tritium gas caused the ionization current to increase. This phenomenon was attributed to the change in the stopping power and W value with the mixing up of different gases.