Optical guide property of alternative He-3 neutron detectors using solid scintillators for nuclear safeguards

Ozu, Akira  ; Nakamura, Tatsuya  ; Takase, Misao; Kurata, Noritaka; Haruyama, Mitsuo; Kureta, Masatoshi   ; Soyama, Kazuhiko  ; Seya, Michio

Alternative He-3 neutron detectors using inorganic solid (ZnS:Ag/10BO) scintillators for nuclear safeguards have been developed in Japan Atomic Energy Agency (JAEA). The detector module is made mainly of three components: an aluminum regular square tube (32 mm 32 mm 300 mm), a rectangular scintillator sheet (39 mm 250 mm) and two PMTs. The scintillator sheet is fit on the diagonal inside the square tube, while the two PMTs are installed at both ends of the tube. At present, the detection efficiency of around 50% of that of the He-3 gas detector has been already achieved. The ray sensitivity of 510 is also obtained. The fundamental performance of the alternative detector is strongly dependent on the optical guide property of scintillation lights inside of the tube. The transport properties of the scintillation lights detected with the PMTs was evaluated by a ray-tracing simulation. The results are discussed in comparison with the experimental results.