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モニタリングポストは, 原子力施設における放射線及び放射性物質の漏えい監視のために有用な装置である。この装置は空間線量率 (μSv/h, nGy/h) や計数率 (cpm, cps) のデータを定期的に提供するものである。著者らはこのようなデータの他に原子力事故の早期の発見, あるいは異常データの的確な解釈に有用なγ線の飛来方向を計測できる新型のモニタリングポストを試作した。この検出器は, 扇形をしたNal (Tl) , CsI (Tl) , BGOの3種類のシンチレータと光電子増倍管より構成される。飛来方向によって, それぞれのシンチレータが作る光電ピークの計数が変化することを利用したものである。低エネルギーの241Am (60keV) , 中エネルギーの133Ba (356keV) , 137Cs (662keV) , 高エネルギーの60Co (1250keV) を用いて, 電磁カスケードモンテカルロシミュレーション (EGS) , 及び実験によってエネルギー領域ごとの方向計測感度の特性を評価した。この結果, 本検出器は広いエネルギー領域においてγ線の飛来方向を計測できることが確認された。

The authors developed a real-time personal neutron dosimeter which could give neutron dose equivalent over wide energy region from thermal to 10 odd MeV by using 2 silicon detectors, fast neutron sensor and slow neutron sensor. The energy response of this dosimeter was evaluated under thermal neutron field, monoenergetic neutron field between 200keV and 15MeV, and moderated 252Cf neutron field. The neutron dose equivalent was estimated by adding neutron dose equivalent below 1MeV given by slow neutron sensor and that above 1MeV by fast neutron sensor. It was verified from various field tests that this dosimeter is able to give neutron dose equivalent within a factor of 2 margin of accuracy in reactor, accelerator, fusion research and nuclear fuel handling facilities. This dosimeter has more than one order higher sensitivity than conventional personal neutron dosimeters and is insensitive to γ-rays up to about 500 mSv/h. This dosimeter will soon be commercially available as a personal dosimeter which gives neutron and γ-ray dose equivalents simultaneously by installing γ-ray silicon sensor.

We have developed an advanced method for enhancement of the sensitivity of dosimeters, in which a modified algorithm of the coherent demodulation technique is introduced. A test gamma-dosimeter was produced, which consists of five pairs of CsI scintillator—photodiodes and four Pb plates, and many experiments were performed using 60 Co gamma sources. The background component was reduced to about 1 133 , and then, gamma rays of 0.06 mR/h = 1.55 × 10 −8 C/(kgh) could be detected against a background of 2.66 mR/h = 6.86 × 10 −7 C/(kgh).

There is a great interest to find nuclear accidents as soon as possible and/or to carry out daily monitoring and control for nuclear facilities from a distance. In order to satisfy these requirements, a direction finding gamma-ray detector has been developed as a monitor of gamma-ray leakage from such facilities. The detector comprises three scintillators made of the same material of sodium iodine with thallium NaI(Tl). Computer simulations and laboratory experiments show the possibility of direction finding of gamma rays with reasonable accuracy.