Directional fast neutron detectors for neutron source surveys over large areas

弘中 浩太  ; 小泉 光生 ; 持丸 貴則*; 高橋 時音; 山西 弘城*; 若林 源一郎*

Hironaka, Kota; Koizumi, Mitsuo; Mochimaru, Takanori*; Takahashi, Tone; Yamanishi, Hirokuni*; Wakabayashi, Genichiro*

Directional fast neutron detection is critical for efficient neutron source surveys in nuclear security applications. In this study, we investigate detector geometries and measurement strategies that enable neutron source localization using plastic scintillation detectors without neutron moderation. Two detector configurations were developed: a rod-shaped scintillator equipped with photomultiplier tubes (PMTs) at both ends and a plate-shaped scintillator instrumented with four PMTs at its corners. Angular response measurements to incident neutrons and rectilinear scanning measurements relative to a neutron source were performed. Both detectors exhibited clear angular dependence in neutron count rates attributable to detector geometry. Rectilinear scanning measurements enabled identification of the point of closest approach to the source along the scan path and estimation of the source--detector distance. For the plate-shaped detector, analysis of relative PMT signal strengths provided additional directional information, enabling three-dimensional localization of the neutron source using a single detector. These results demonstrate that plastic scintillation detectors, when combined with appropriate geometries and scanning strategies, can achieve neutron source localization --- which is a key capability for mobile neutron source survey applications.