Tritium measurement system utilizing an ionization chamber is widely used but the memory effect often gives obstruction for accurate measurement. We designed a method of tritium removal from electrode surface utilizing an isotope exchange reaction, namely, water vapor mixing to the process gas just before entering the ionization chamber, and good results were observed for an ionization chamber made of copper or stainless steel. In case of the ionization chamber having stainless steel electrodes, smaller memory effect, though larger amount of tritium sorption, was observed than for the copper chamber, because of porous Fe3O4film formed on stainless steel surface.
Measurement was made to determine self-dose at Mihoro Dam Tunnel where cosmic-ray was fairly attenuated. The dosimeter with Pb and Sn filter had the same self-dose of 0.26 nCkg-1h-1as that without the filter. Our experiment shows that self-dose is due to any traces of natural radioactivity in the phosphor and the packaging. Cosmic-ray dose was evaluated 0.74 nC kg-1h-1from our experiment at sea surface, and this value was somewhat smaller than the cosmic-ray intensity in Japan. The reason is considered to be low TL response for cosmic-ray hard component.