As reported in the Asahi:
The science ministry has begun posting real-time radiation levels on its website at 2,700 locations across Fukushima Prefecture, including schools and parks.http://ajw.asahi.com/article/behind_news/social_affairs/AJ201202220028
To access radiation levels measured at 10-minute intervals, go to http://radiomap.mext.go.jp/ja/.
A picture of the equipment:
https://dwqovw6qi0vie.cloudfront.net/article-imgs/en/2012/02/22/AJ201202220028/AJ201202220029M.jpg
Checking out today's data at
http://radioactivity.mext.go.jp/map/ja/area.html
Let's do some math...
Consider the maximum acceptable radiation dose for the public from any man-made facility: 1 mSv/year.
1 mSv/year is 1000 μSv/year.
1000 μSv/year is 0.114 μSv/h.
(Based on 8766 hours in a year (24×365.25) and 1000 microsieverts(μSv) in a millisievert (mSv).
Therefore any place with over 0.114 μSv/h is questionable.
Japan set a limit 20 times higher, 20mSv/year, for Fukushima residents.
Residents exposed at that level would reach the 350 mSv/lifetime limit which was used to determine evacuation areas after the Chernobyl disaster within 18 years.
Using the Chernobyl lifetime standard, calculating for a 10-year old child with an additional 70 years life expectancy, 350mSv/70years = 5mSv/year.
Recapping, the 1 mSv/year international standard is exceeded by the Chernobyl evacuation standard, which (if judged to be tolerable) could conceivably justify 5 mSv/year for kids (twice that for 35-year-olds, etc.), and that was exceeded by the 20 mSv/year Japanese Fukushima-only standard, which I believe was set at that level for political reasons only, to set a standard that would avoid the need to evacuate several large cities and partially sever northern Japan from the south and middle.
Some selected ranges of readings for locations today, Sunday, April 29, 2012:
Fukushima-ken locations:
MinamiSoma 0.080 - 5.036 μSv/h = 0.701 - 44.14 mSv/year
Fukushima City 0.092 - 1.764 μSv/h = 0.806 - 15.46 mSv/year
NihonMatsu 0.113 - 1.324 μSv/h = 0.990 - 11.60 mSv/year
Koriyama 0.067 - 1.379 μSv/h = 0.587 - 12.08 mSv/year
Sukagawa City 0.098 - 0.727 μSv/h = 0.859 - 6.372 mSv/year
Soma City 0.093 - 1.125 μSv/h = 0.815 - 9.862 mSv/year
Iwaki City 0.054 - 0.819 μSv/h = 0.473 - 7.179 mSv/year
Aizu-Wakamatsu 0.054 - 0.290 μSv/h = 0.473 - 2.542 mSv/year
Outside Fukushima-ken:
Tochigi-ken 0.036 - 0.593 μSv/h = 0.315 - 5.198 mSv/year
Miyagi-ken 0.033 - 0.367 μSv/h = 0.289 - 3.217 mSv/year
Ibaraki-ken 0.048 - 0.178 μSv/h = 0.420 - 1.560 mSv/year
Chiba-ken 0.037 - 0.172 μSv/h = 0.324 - 1.507 mSv/year
Gunma-ken 0.026 - 0.154 μSv/h = 0.228 - 1.349 mSv/year
Saitama-ken 0.027 - 0.154 μSv/h = 0.236 - 1.349 mSv/year
Tokyo-to 0.037 - 0.064 μSv/h = 0.324 - 0.561 mSv/year
If you use the lifetime-exposure evacuation standard for Chernobyl applied to children, all children should be evacuated from all of the cities measured in eastern Fukushima prefecture, with the exception of Aizu-Wakamatsu, which is more central, but which still exceeds the 1 mSv/year international standard for the nuclear power industry. Some sites in Tochigi prefecture also exceed the Chernobyl standard and should evacuate children.
All of these prefectures in the Kanto region have at least a few MEXT radiation measurement stations (which are very limited in number outside Fukushima, by the way, 5 stations in Tokyo, 7 in Chiba, etc) which record levels above the 1 mSv/year international standard. By that standard, Kanto is barely tolerable.
Numbers here in Chiba:
html at http://radioactivity.mext.go.jp/html/12/12000.html
2012年04月29日 20時00分時点
In Chiba, Kashiwa (柏市) and Inzai (印西市) both exceed the 1 milliSievert/year limit for added radiation from nuclear power.
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