原子力災害時における車両汚染検査の最適化手法の研究,1; 既存の可搬型車両用ゲート型モニタによる測定迅速化

Study on optimization method for contamination inspection of vehicles in nuclear emergency, 1; Quick measurement by existent portable radiation portal monitors for vehicles

平岡 大和  ; 川崎 晃平*; 木村 仁宣 ; 外川 織彦 ; 齊藤 将大 ; 江崎 巌*

Hiraoka, Hirokazu; Kawasaki, Kohei*; Kimura, Masanori; Togawa, Orihiko; Saito, Shota; Ezaki, Iwao*

原子力災害時に避難住民が受ける汚染検査では、多数の車両による混雑が予想される。検査の迅速化には可搬型車両用ゲート型モニタ(ゲートモニタ)を活用したタイヤとワイパー部の同時測定が課題であるため、両者からの計数率の弁別を試みた。初めに、車両を5km/hで走行させ、ゲートモニタを通過する間の線計数率を測定した。このとき、汚染を模擬したBa線源を車両のタイヤ周囲又はワイパー部に取り付け、それぞれ30回ずつ測定した。次に、測定値(Net値)の最大計数率を1.0とした規格化計数率に一次関数を基準とした弁別条件を適用し、タイヤとワイパー部の弁別精度を評価した。評価の結果、タイヤ周囲に線源を設置したパターンでは30回中29回、ワイパー部に設置したパターンでは30回中20回正しく弁別できた。弁別の精度を高めるには、タイヤとワイパー部の間で大きな差異が生じるような測定手法の改良が求められることが分かった。

When the nuclear emergency occurs, inhabitants take the contamination inspection to evacuate. A large number of vehicle will come to the inspection area and make there congested. To do the quick inspection, simultaneous measurement of tires and wipers using the portable radiation portal monitors for vehicles is a key point. Consequently, we attempted the count rates obtained from tires and wipers are discriminated. First, the vehicle was driven at 5 km/h and the -ray counts rate was measured by the monitor. Ba sources were attached around the tire or on the wiper and measurements were taken 30 times each. Next, discrimination conditions based on a linear function were applied to the normalized count rates, with the maximum count rate of the measured values (Net value) set to 1.0, to evaluate the discrimination accuracy between the tire and the wiper. The evaluation results showed that the pattern with the source attached around the tire correctly discriminated 29 out of 30 times, while the pattern with the source attached on the wiper correctly discriminated 20 out of 30 times. It was found that in order to improve the accuracy of discrimination, the measurement method must be improved so that there is a large difference between measured values of the tire and the wiper.