Standardization of Tritium Measuring Devices Based on a High-Sensitivity Calorimeter

A twin type thermal conduction calorimeter has been specially designed and constructed for absolute measurement of tritium, and then its performance was examined using two kinds of tritium samples, i.e., ZrNi alloy powders loaded with a given amount of tritium. Total amounts of tritium in the ZrNi alloy powders were previously estimated by a small ionization chamber. Changes in radioactivity of two samples were followed for three years, and it was seen that the activity changes obeys the half-life of 4505 days. The initial tritium amounts estimated by the small ionization chamber agreed well with the extrapolated values from the activity changes evaluated by the calorimeter. Namely, it was suggested that the small ionization chamber is able to be used as a secondary standard of the tritium measuring devices. The -ray-induced X-ray counter was also calibrated for non-destructive measurements of high-level tritium by using the present small ionization chamber.