Development of the Multi-Cubic γ-ray spectrometer and its performance under intense 137Cs and 60Co radiation fields

Abstract

Abstract The number of nuclear facilities being decommissioned has been increasing worldwide, in particular following the accident of the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Station in 2011. Large amounts of radioactive wastes and spent nuclear fuels are stored in these facilities. Furthermore, advanced radiation therapies such as proton therapy, ion therapy, and boron neutron capture therapy using charged-particle accelerators have become popular, but charged-particle accelerators generate radiators during operation. In these nuclear and radiation facilities, proper management of radioactive materials is required until the end of the deactivation, cleanup, or disposal. Then, γ -ray spectroscopy techniques have been useful tools because they can obtain significant information on radioisotopes. Besides, space information of radioisotopes is also important, and γ -ray imaging is also required. However, intense radiation fields are located at these facilities, causing γ -ray spectroscopy and imaging difficultly. A γ -ray spectrometer with four segmentations using small-volume CeBr 3 scintillators with a dimension of 5 × 5 × 5\xa0mm 3 was developed. The four scintillators were coupled to a multi-anode photomultiplier tube specific to intense radiation fields by individual supplied voltages to the last three stages. We performed the γ -ray exposure study under 137Cs and 60Co radiation fields at the National Institute of Advanced Industrial Science and Technology in Japan. Under the 137Cs radiation field, the relative energy resolution at 1375 mSv/h was 9.2\xa0±\xa00.05%, 8.0\xa0±\xa00.08%, 8.0\xa0±\xa00.03%, and 9.0\xa0±\xa00.04% for the four channels, respectively. As the dose rate increased, significant spectral downward shifts were observed for the four channels under the 137Cs and 60Co radiation fields because of the space charge effects in the photomultiplier tube. However, the Multi-Cubic sensor could provide the total throughput rate for the four channels of greater than 6 Mcps (Mcps: 106 counts per second), which increases the detection efficiency under intense radiation fields.