– Ministry of Education Maps of Plutonium and Strontium Show Wide Dispersion of Supposedly Heavy Nuclides (EX-SKF, Sep. 30, 2011):
On September 30 the Ministry of Education and Science posted the blurry maps plotting the locations where plutonium and strontium have been detected.
(On the same day, September 30, the national government abolished the evacuation-ready zone between the 20 and 30 kilometer radius from the plant, “allowing” the residents to return.)
The Ministry’s 10-page document is in Japanese only for now.
According to the Ministry, the survey for plutonium and strontium was carried out in early June to early July in 100 locations within the 80-kilometer radius from Fukushima I Nuclear Power Plant by government researchers. One location each in 59 municipalities within the 80-kilometer radius was picked, based on the air radiation level and the high population density. The remaining 41 locations were picked from within the 20-kilometer radius evacuation zones.
The Ministry claims it is the first time plutonium has been detected outside the plant, but all that means is that it is the first time a government ministry has admitted to the existence of plutonium outside the plant. As the readers of this blog already knows, as early as April the researchers were taking soil samples outside the plant and have them tested for plutonium and found it (see here and here).
The Ministry’s conclusion is that the amount of plutonium is not that big to cause any alarm, and that they should focus more on the decontamination of cesium-134 and -137.
As for strontium, the Ministry does sound a bit more nervous. It says the ratios of radioactive strontium to cesium-137 in these locations were calculated; the ratios varied too much, indicating there was no correlation between the deposition of radioactive strontium and radioactive cesium. The Ministry will conduct further, more detailed study in locations that had higher strontium ratios.
Plutonium-238 (top number in the map), Plutonium-239+240 (bottom number):
Strontium-89 (top number in the map), -90 (bottom number):