Gamma-ray spectroscopy with a CeBr₃ scintillator under intense γ-ray fields for nuclear decommissioning

Recently, an increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Station. However, large amounts of radioactive wastes and spent nuclear fuels remain on these facilities, leading to intense radiation fields. During the decommissioning processes, radioactive wastes and spent nuclear fuels have to be retrieved under proper management, and γ-ray spectroscopy supports this process. In this study, a small cubic CeBr₃ spectrometer with dimensions of 5 mm × 5 mm × 5 mm was manufactured to perform γ-ray spectroscopy under intense γ-ray fields. Furthermore, thanks to both: (1) a digital process unit with sampling rate of 1 Giga samples per second; and, (2), a photomultiplier assembly featuring individual voltages supplied to the last three stages; the device successfully performed γ-ray spectroscopy up to at dose rates of over 1 Sv/h. The energy resolution (full width at half maximum) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a ¹³⁷Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a ⁶⁰Co radiation field. The energy resolution met the requirements to solve the prominent γ-ray spectral lines of ¹³⁴Cs, ¹³⁷Cs, ⁶⁰Co, and ¹⁵⁴Eu. These results suggest that the detector has the potential to realize the γ-ray assessment of ¹³⁴Cs, ¹³⁷Cs, ⁶⁰Co, and ¹⁵⁴Eu at dose rates of over 1 Sv/h.