The thyroid glands of children in Fukushima Prefecture were exposed to radiation doses of up to 35 millisieverts following the accident at the Fukushima No. 1 nuclear power plant, the Nuclear Safety Commission of Japan said Feb. 21.
The estimate is based on results collected in Iwaki, Fukushima Prefecture, late last March, but not released by the government at the time.
The government's local response headquarters tested the thyroid glands of 1,080 children in Fukushima Prefecture on the advice of the commission. According to materials released by the commission, 11 of 137 under the age of 15 checked in Iwaki had relatively high radiation doses in their thyroid glands of 5 to 35 millisieverts. The second highest dose was 25 millisieverts and the third-highest dose was 21 millisieverts.
The government did not release the figures, arguing that the measurements were too inaccurate.
The International Atomic Energy Agency's standard for the intake of stable iodine tablets to prevent radiation exposure in the thyroid gland is 50 millisieverts in the case of 1-year-old infants. None of the subjects exceeded that level.
The Fukushima prefectural government on Feb. 20 released the results of a survey in which external radiation doses were estimated for 10,468 residents in the prefecture. The maximum whole-body dose was 23 millisieverts among the 9,747 residents who were not nuclear plant workers.
The latest release by the commission relates to topical doses in thyroid glands. According to a formula adopted by the International Commission on Radiological Protection, the values can be divided by 25 to produce external radiation doses for the whole body.
The commission said that it advised the government's Nuclear Emergency Response Headquarters late last March to conduct additional surveys on children with high doses, but that the recommendation was rejected on the grounds that such measures could cause alarm among the children and their families.
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