Construction of the standard system for absolute measurement of tritium

点击翻译按钮获取中文摘要

To evaluate the absolute amount of tritium, a calorimetric system was designed and constructed, and its basic performance has been tested. The calorimetric system is applicable to measure solid, liquid and gaseous tritium. For this application the present calorimetric system is equipped with a high sensitivity calorimeter, a tritium container, total pressure gauges, a quadrupole mass spectrometer, and high vacuum systems. A twin type thermal conductivity calorimeter with a vacuum shielding was specially employed for the present purpose. A calibration curve of the calorimeter has been prepared at first using solid materials absorbed a given amount of tritium, and the following linear relation was obtained : E_<out>=(0.2694±0.0010) Q_<in>, where E_<out> describes the output (μV) from the heat sensors and Q_<in> the input power (μW) by Joule heating to the sample cell. In addition, the lower detection limit was estimated to be 0.15μW from stability of the calorimeter, which corresponds to the tritium amount of 0.16 GBq. As the first test, Zr-Ni alloy powder loaded with a given amount of tritium was measured by the calorimeter and the amount of tritium was evaluated to be 26.3 GBq, which was a little lower than the tritium activity determined previously by using a small ionization chamber. The second test was applied to measurement of tritiated water. The observed calorific value was about ten times greater than that of the expected value. It was seen that this is due to the oxidation reaction of a liquid cell with oxygen dissolved into tritiated water. Improvement of a liquid cell will lead to successful measurements of tritium.