Development of a Twin Type Conduction Calorimeter with a Vacuum Chamber for Radioactivity Measurements

概要

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A twin type conduction calorimeter having a vacuum chamber was developed for high sensitive measurements of radioactivity of radionuclides with lower noise level and smaller baseline drift. The object of present experiment was to investigate the effect of low pressure (around 0.67Pa) atmosphere on the thermal noise and baseline drift of the calorimeter output. The results showed lower thermal noise, 0.015μV p-p, (0.09μW), smaller baseline drift, 0.015μV p-p, (0.135μW), and higher sensitivity, 0.17μVμW1 in comparison with a conventional calorimeter operated in the atmospheric pressure.Small amount of thermal power evolved from the radioactive sample of carbon-14 (Ba14Co3) sealed in a glass vial was non-destructively measured using this calorimeter.The radioactivity of C-14 was determined from the measured thermal output of 3.56μW±1.58% (standard deviation) and its overall uncertainty was estimated by considering various factors. Consequently the result was found to be 450MBq (12mCi)±4.9% (in 99.7% credibility limit). The result suggested more than 10 times improvement in sensitivity of radioactivity measurement was attained.
日本熱測定学会の論文