A Monte Carlo simulation to study a design of a -ray detector for neutron resonance densitometry

中性子共鳴濃度分析法に使われる線検出器の設計のためのモンテカルロシミュレーション

土屋 晴文 ; 原田 秀郎   ; 小泉 光生 ; 北谷 文人  ; 高峰 潤 ; 呉田 昌俊   ; 飯村 秀紀  

Tsuchiya, Harufumi; Harada, Hideo; Koizumi, Mitsuo; Kitatani, Fumito; Takamine, Jun; Kureta, Masatoshi; Iimura, Hideki

Neutron resonance densitometry (NRD) has been proposed to quantify nuclear materials in melted fuel (MF) that will be removed from the Fukushima Daiichi Nuclear Power Plant. Those MFs probably involve impurities of non-nuclear materials, and would prevent us from accurately measuring nuclear materials. Thus, NRD is based on a combination of neutron resonance transmission analysis (NRTA) and neutron resonance capture analysis (NRCA). The latter would enable us to identify impurities with their prompt rays. Here, a design study of a -ray detector for NRCA in NRD was performed with Geant4. In order to effectively detect the prompt rays, the -ray detector has a well shape, consisting of a cylindrical and a tube type LaBr scintillators. We show how the -ray detector measures 478 keV rays derived from B in MF under a high radiation environment caused by Cs. It was found that the -ray detector was able to well suppress the Compton edge derived from Cs by using the tube type scintillator as a back-catcher detector. Then, we demonstrate that with this ability, detection of 478-keV rays derived from B is accomplished in realistic measuring time, and that achievable statistical uncertainty strongly depends on boron concentration in MF.