Development of an alpha particle spectrometer based on a GPS scintillator plate based for high-reliable dust monitor

GPSシンチレータプレートを用いた高信頼性アルファ線ダストモニタの開発

森下 祐樹   ; 金子 純一* ; 井崎 賢二 ; 矢島 辰雄*; 松浦 貢*

Morishita, Yuki; Kaneko, Junichi*; Izaki, Kenji; Yajima, Tatsuo*; Matsuura, Mitsugu*

事故時に放出されるPuやPuの空気汚染の検知のため、シリコン半導体検出器を用いたダストモニタが原子力施設に設置されている。しかし、このダストモニタは誤警報を頻発していた。高信頼のダストモニタの開発のため、GPSシンチレータとPMTを用いた線スペクトロメータを開発した。5.5MeV線に対するエネルギー分解能を評価した結果11.9% FWHMであった。ラドン子孫核種の除去率はZnS(Ag)シンチレータを用いた線スペクトロメータより向上した。今後開発したスペクトロメータは高信頼のダストモニタへの応用が期待できる。

For detecting airborne contamination of Pu and Pu released by the accident, a dust monitor with a silicon surface barrier detector (SSBD) is introduced at a site of nuclear fuel facility. However, SSBD frequently produces a false alarm triggered by an electromagnetic noise generator. For high-reliable dust monitoring, we developed an particle spectrometer based on the GPS scintillator plate with PMT. Our developed spectrometer consists of a cerium doped GdSiO (GPS) scintillator plate and a Photomultiplier Tube (PMT). The GPS scintillator plate was hexagonal in shape and 50 mm in diameter and a scintillator layer was approximately 40 um. An Am source with 5.5 MeV particle, Rn progeny collected air filter, and PuO particle were measured by developed spectrometer. The energy resolution for 5.5-MeV particles was 11.9% FWHM. The radon progeny nuclide reduction ratio (Rratio) was improved compared with ZnS(Ag) based spectrometer, so that Pu and Rn progeny can be effectively distinguished. Thus, our developed spectrometer will be high-reliable dust monitor for detecting Pu contamination.