(More information in the new post.)
The Nuclear Safety Commission headed by Haruki "Detarame" Madarame disclosed on July 4 that the test conducted in late March had found 45% of 1,080 children tested in Fukushima Prefecture had internal radiation exposure at thyroid gland, according to Tokyo Shinbun.
3 months, that seems to be the amount of time that these government people must feel safe to disclose what they had known all along. After 3 months, people may forget, and/or people will give up because the disclosure is too late.
The NSC says the levels were low, and there was no need for more detailed evaluation.
If you look at the numbers, though, you may wonder how they came to the conclusion. To them, 100 millisieverts per year body dose equivalent for 1 year old (or 0.2 microsievert/hour) was acceptable because the ICRP says so. Since the highest they found was 50 millisieverts per year body dose equivalent, they concluded there was no need for further testing.
From Tokyo Shinbun (7/5/2011):
東京電力福島第一原発の事故で、国の原子力安全委員会は四日、三月下旬に福島県内の第一原発周辺の市町村に住 む子供約千人を対象に行った放射線被ばく調査で、４５％の子供が甲状腺に被ばくしていたことを明らかにした。安全委の加藤重治審議官は「精密検査の必要は ないレベル」と話している。
Japan's Nuclear Safety Commission disclosed on July 4 that the survey done in late March on 1,000 children living near Fukushima I Nuclear Power Plant had revealed that 45% of the children were exposed to radiation at the thyroid gland. Commissioner Shigeharu Kato says "The radiation level was not the level that would require more detailed examination."
The survey was conducted by the national government and the Fukushima prefectural government from March 26 to 30 in Iwaki City, Kawamata-machi, and Iitate-mura, where the authorities expected the high probability of internal radiation exposure at the thyroid gland. 1,080 children aged zero to 15 were tested, and 45% had the internal radiation exposure.
安全委によると、最高値は毎時〇・一マイクロシーベルト（一歳児の甲状腺被ばく量に換算すると年五〇ミリシーベルト相当）に上ったが、９９％は毎 時〇・〇四マイクロシーベルト以下。同様の換算で年二〇ミリシーベルトに相当するが、加藤審議官は四日の記者会見で「換算するには（調査の）精度が粗い。 精密測定が必要な子供はいなかった」と述べた。
According to the NSC, the highest dose was 0.1 microsievert/hour (body dose equivalent of 50 millisieverts per year at thyroid gland for 1 year old). For 99% of the children tested, the dose was 0.04 microsievert/hour or less, which is the dose equivalent of 20 millisieverts per year at thyroid gland for 1 year old. However, Commissioner Kato said in the press conference on July 4, "To consider body dose equivalent, the survey was too coarse. There was no child who need further detailed examination."
国際放射線防護委員会（ＩＣＲＰ）勧告では、年間一〇〇ミリシーベルトの被ばくで発がんリスクが０・５％高まるとして、同量を緊急時の年間被ばく 限度としている。今回の調査でも一〇〇ミリシーベルトを基準とし、一歳児の甲状腺被ばくの年換算でこれに相当する毎時〇・二マイクロシーベルトを超えた場 合、精密検査をする予定だった。
According to the ICRP recommendation, 100 millisieverts per year will increase the risk of cancer by 0.5%, and that amount is set as the maximum annual exposure limit in a nuclear emergency. In the survey this time, the standard was set at 100 millisieverts, and the detailed examination was to be done if 0.2 microsievert/hour dose was found, which would be the dose equivalent of 100 millisieverts per year at thyroid gland for 1 year old.
The Japanese government submitted the report to the IAEA which mentioned the survey done on 1,080 children for radiation at the thyroid gland, but the government did not disclose what percentage of the children were actually affected.
So the Japanese government was secretly testing the children in Iitate-mura, as it scoffed at the suggestion by IAEA that the radiation level in the village was very high and evacuation should be considered. All back in late March when it could have made a difference.
According to Tokyo Brown Tabby who read the Japanese post and called up the NSC, the NSC says the data was uploaded in May to the NSC website. So far I haven't managed to locate it. The NSC also says they informed the parents. I hope so.