and

H. Sato

Research and Development Laboratory, Aloka Co. Ltd. 1-22-6 Mure, Mitaka, Tokyo, Japan The contamination of three ionization chambers(Cu, Ni-plated, and Au-plated chambers) due to exposure to HT or HTO was measured. Considerable contamination took place for all of the chambers due to exposure to HTO. This is caused by the physical adsorption of HTO. The extent of the contamination differed from each other (Ni > Au > Cu), being considered due to difference in their surface roughness. In case of the exposure to HT, the Cu-chamber was contaminated in room air, whereas the Ni-chamber did in dry air atmosphere. This is considered due to the adsorption of HTO (being formed with catalytic exchange reaction between HT and H2O) on the Cu-chamber and that of HT on the Ni-chamber. The Au-chamber was not contaminated with the exposure to HT. This is because neither the adsorption of HT nor the catalytic exchange reaction takes place on this surface.