Development of a low-level tritium monitor in the air dividing chemical form 2

In the air, there are three chemical species which contain tritium. We are developing a tritium monitor which is directly able to measure the tritium concentration of the species; water vapor, molecular hydrogen and methane in the environmental air. The specific activity of tritium in the water vapor is too low to measure directly using conventional technique. The abundance ratios of molecular hydrogen and methane in the air are about 0.5 ppm and 2 ppm respectively. And their tritium concentrations are about 25mBq/m3-air and 12mBq/m3-air respectively. Then their specific activities are very high compared with the value of water vapor. Then the tritium concentrations would be measured, if the molecular hydrogen were collected. We have carried out several series of experiment using a high-polymer gas permeable membrane and palladium based alloy hydrogen permeable membrane. Based on the result, we have conceptually designed a tritium monitor as follows. (1) The air intake is 3.2 NL/min. (2) The detector is a proportional counter. (author)