GEANT4 simulation study of a -ray detector for neutron resonance densitometry

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

We have proposed a system to quantify nuclear materials in melted fuels in the reactors of the Fukushima Daiichi Nuclear Power Plant. The system utilizes non destructive techniques combining neutron resonance transmission analysis (NRTA) and neutron resonance capture analysis (NRCA). This is because the melted fuels are though to involve not only nuclear materials but also impurities such as Hydrogen, Boron, Zirconium, and Iron. Using the combined system, we would be able to identify those non-nuclear materials by NRCA and accurately measure nuclear materials by NRTA. A -ray detector for NRCA consists of a cylindrical LaBr scintillation counter and a well-type LaBr one. The well-type counter is served as a back-catcher detector and individual signals recorded in the two counters are summed to aim at reducing the Compton edge originating from Cs that generate intense background for the NRCA measurement. According to GEANT4 simulation, It can be seen that the Compton edge is suppressed by the well-type counter. For example, thanks to the well-type counter, a count at an energy of B-derived -rays (478 keV) is reduced by 0.15. In this presentation, we show performance of the -ray detector using GEANT4 simulation. In addition, comparing results based on evaluated cross sections of ENDF-VII.0 with those based on JENDL-4.0, we discuss differences in performance expected for the -ray detector.