The staff stayed in Fukushima prefecture for 3–4 days per dispatch, working at evacuation sites during the day and staying at a hotel near Fukushima City at night. As shown in Tables 17.1 and 17.2, Screening Team 1 had the largest accumulated dose from external exposure and internal exposure caused by iodine and cesium. Their dispatched period was the earliest; moreover, they used only simple masks with casual clothing so as not to make the evacuees anxious, so there was little difference in protection from internal exposure between staff members and evacuees. On the basis of the internal radiation dose of the first dispatched team, we gave the next dispatched team a warning to protect against internal exposure. The decrease in internal radiation doses after the second team was dispatched is attributable to the warning statement to the dispatched staff of KURRI regarding protection against internal radiation.
Fig. 17.3 The activity of 134Cs + 137Cs measured by KURRI whole-body counter. Diamond symbols show the activity of 134Cs + 137Cs of volunteer A. Square symbols show the activity of 134Cs + 137Cs of volunteer B. Black arrows show the dispatched period of Volunteer A. White arrows show the dispatched period of Volunteer B
Between September 2011 and March 2012, the internal radiation exposure of cesium in the 9,498 evacuated residents of Minamisoma, located 23 km north of the TEPCO plant, was measured. It was reported that the committed effective doses were less than 1 mSv in the 9,497 residents (Tsubokura 2012). We confirmed that internal exposure to cesium and iodine radiation soon after TEPCO's nuclear power
plant accident was relatively low; that is, the largest effective dose was 39 μSv in the 59 dispatched KURRI volunteers. We are not aware of any published report on
follow-up data of the internal exposure to cesium and iodine radiation measured with a whole-body counter in public after the early period following the TEPCO Fukushima Daiichi nuclear power plant accident.
The follow-up data of internal doses for two volunteers of the first dispatched team showed that the activity of iodine-131 was detected for 40 days in volunteer A and for 9 days in volunteer B after the last dispatch working day in Fukushima prefecture. Cesium-137 and -134 of volunteer A has been detected for 125 days and that in volunteer B for 56 days after the last dispatch working day in Fukushima.
The American Nuclear Society reported the initial measurements for residents who lived in areas associated with high doses of Fukushima Prefecture. Between June 27and July 16 in 2011, the activities of cesium-134, cecium-137, and iodine-131 were measured in 122 residents by whole-body counter. Cesium-134 was detected
47.7 % and cesium-137 at 29.4 %; the highest activity was 3,100 Bq of cesium-134 and 3,800 Bq of cesium-137. Iodine-131 was not detected. Based on this internal radiation measurement, the combined internal dose was less than 1 mSv for residents (ANS Committee Report 2012). Similar to the internal radiation data of the residents living near the high-dose area in Fukushima, the activity of iodine-131 in two volunteers was not detected at the end of June 2011. The activities of cesium-137 and -134 of volunteer A and volunteer B on 2011/8/8 were measured as 1,714 and 789 Bq, respectively. It is reported that the half-life in the human body of episodic ingestion of cesium was 100 days. When a human intakes cesium chronically, cesium accumulates in the body and reaches equilibrium (ICRP Publication 2009). The activities of cesium of volunteer A continued rather higher 138 days after the initial dispatch because he had visited Fukushima several times in the earlier period following the TEPCO Fukushima Daiichi nuclear power plant accident.
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