||A survey on the accuracy of whole-body counters operated in Fukushima after the nuclear disaster
仲野, 高志 ,
谷, 幸太郎 ,
金, ウンジュ ,
栗原, 治酒井, 一夫
Significant amounts of radionuclides were released into the environment due to the Fukushima Daiichi nuclear power station accident in March 2011. These radionuclides were deposited on the ground of wide areas of eastern Japan and a number of evacuees still cannot return home because of relatively high air dose rates caused by radioactive caesium (Cs-134 and Cs-137) on the ground. Compared to external exposure, internal exposure is much smaller under current radiation situations in Fukushima. Internal dose measurements with whole-body counters (WBCs) have been continued since late June in 2011 and the number of subjects being examined exceeded two hundred thousand so far. To cope with these extensive measurements, many WBCs have been newly installed; most of them are standing -type WBCs (FASTSCAN, Canberra Inc., US). National Institute of Radiological Sciences was requested to check the accuracy of 36 WBCs in FY 2012 and 2013. This task was performed using a set of BOMAB phantoms, each of which contains Ba-133, Cs-137, Co-60 or water, separately. These phantoms imitate an adult male (177 cm in height and 70 kg in weight) and the activity amounts in the phantoms were certificated by Japan Calibration Service System (JCSS). As a result, the relative error to the BOMAB phantoms ranged from -15% to 15% for Cs-137 (36 WBCs) and Co-60 (33 WBCs). The relative error was distributed positive-negative symmetrically for Cs-137, whereas was biased to the negative side for Co-60. Some WBCs could not identify Co-60 and/or Ba-133 because these nuclides were not originally intended to measure. Significant problems were not found in the WBCs being examined; however, it is necessary to develop some system to maintain the accuracy of around 50 WBCs currently operated in Fukushima.
国際学会IM2015(International Conference on Individual Monitoring of Ionising Radiation)