Development of whole energy absorption spectrometer for decay heat measurement

The Whole Energy Absorption Spectrometer (WEAS) has been developed as a new experimental instrument for decay heat measurements. The WEAS consists of a pair of large bismuth–germanate (BGO) scintillators of 120 mm diameter and 100 mm thickness, and both beta- and gamma-rays emitted from a sample can be measured simultaneously with a detection efficiency close to 100%. To demonstrate feasibility of decay heat measurements with WEAS, an experiment was performed. Sample materials were irradiated by 14-MeV neutrons and decay heat arisen in the samples were measured with WEAS. As a result, decay heat data in a wide cooling time period from 1 min to 400 days were obtained successfully with typical accuracy of 6–10%. It was found that WEAS had many excellent features such as high sensitivity, resistivity for high counting rate measurement and wide dynamic range. An application of WEAS for decay Q-value measurements was also demonstrated.