LaBr₃ γ-ray spectrometer for detecting ¹⁰B in debris of melted nuclear fuel

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• 作者：Mitsuo Koizumi^a ; ^{koizumi.mitsuo@jaea.go.jp" class="auth_mail" title="E-mail the corresponding author} ; Harufumi Tsuchiya^a ; Fumito Kitatani^a ; Hideo Harada^a ; Jan Heyse^b ; Stefan Kopecky^b ; Willy Mondelaers^b ; Carlos Paradela^b ; Peter Schillebeeckx^b
• 关键词：Nuclear resonance densitometry (NRD) ; Neutron resonance transmission analysis (NRTA) ; Prompt gamma ray analysis (PGA) ; 10B ; LaBr3 ; Scintillation detector
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2016
• 出版时间：21 November 2016
• 年：2016
• 卷：837
• 期：Complete
• 页码：153-160
• 全文大小：1405 K

文摘

Neutron resonance densitometry has been proposed as a nondestructive analytical method for quantifying special nuclear material (SNM) in the rock- and particle-like debris that is to be removed from the Fukushima Daiichi nuclear power plant. The method is based on neutron resonance transmission analysis (NRTA) and neutron resonance capture analysis combined with prompt-γ-ray analysis (NRCA/PGA). Although quantification of SNM will predominantly rely on NRTA, this will be hampered by the presence of strong neutron-absorbing matrix materials, in particular ¹⁰B. Results obtained with NRCA/PGA are used to improve the interpretation of NRTA data. Prompt γ rays originating from the ¹⁰B(n, αγ$\alpha \gamma$) reaction are used to assess the amount of ¹⁰B. The 478 keV γ rays from ¹⁰B, however, need to be measured under a high-radiation environment, especially because of ¹³⁷Cs. To meet this requirement, we developed a well-shaped γ-ray spectrometer consisting of one cylindrical and four rectangular-cuboid LaBr₃ scintillators combined with a fast data-acquisition system. Furthermore, to improve the gain stability of the main detector, a special high-voltage divider was developed. Because of the reduction in gain shift, a 3.8% resolution at 662 keV was obtained for long-term measurements. By using the data-acquisition system, which consists of eight 250 MHz digitizers, input signals of over 500 kHz per channel were recorded. The work reported herein demonstrates that, with such a spectrometer, the impact of the Compton edge of 662 keV γ rays from ¹³⁷Cs is significantly reduced, which allows the ¹⁰B amount to be determined with greater sensitivity.