This paper describes a differential ionization chamber system which measures a wide-range concentration of tritium gas without being affected by the tritium contamination of the chamber wall. Since tritium is easily adsorbed to or into the wall, the detection level of tritium gas is raised. The differential ionization chamber system consists of a spherical and a cylindrical chamber. The inner walls of the two chambers are made of the same material and have identical surface areas.
With this pair of chambers, it is possible to cancel currents, which are produced by β-rays from the accumulated tritium gas on the chamber wall. Experiments show that gas-borne tritium can be measured over a range of concentration from 3.7 × 10^-2 to 3.7 × 10⁴ Bq/cm³ in real time.