The Japanese government has issued a contour map showing cumulative radioactive dose in air in the 50 km or so of northeastern Japan around the Fukushima Daiichi site, to 11 September. Also displayed on the map are the 20km mandatory and 30km optional evacuation radius circles.
The map shows that the highest radiation dose falls in a familar plume heading northwest from the power station, which is on the coast, and that as would be expected the highest levels of contamination are in the vicinity of the station, more distant areas generally having been exposed to lower doses. However, radiation dose does not simply drop away with increasing distance. The information on which the map is based and th map itself show three pockets of higher radioactivity (greater than 50 mSv) within the 20km zone, and one outside it. The standard IAEA maximum safe radiation dose for the general population is 1 mSv/year (the worldwide average background radiation is about 2.5 mSv/year).
The map is based on sampling radiation at many points.
A copy of the map and regular Fukushima updates may be found on the website of our sister journal, Nuclear Engineering International, reachable on <www.neimagazine.com> or by clicking on the link in the navigation bar to the left of this page.
The following sites are also posting continuing updates:
<http://www.tepco.co.jp/en/index-e.html>
<http://www.iaea.org/>
<http://www.jaif.or.jp/english/>
<http://bravenewclimate.com/2011/03/15/tepco-reactor-status/>
<http://www.world-nuclear-news.org/>
<http://www.kantei.go.jp/foreign/index-e.html>
