Comment Here's the letter and data (Score 5, Informative) 164
http://olympicsokuteikai.web.fc2.com/encontents.html
Perhaps the most crucial part of the letter is this:
"Just before the Fukushima power plant accident, the mean value of the atmospheric radiation in Tokyo was estimated as 0.04 Sv/h, and radioactive Cesium was almost non-existent. Therefore, atmospheric radiation value above this level can be regarded as the effect of the nuclear accident."
Is that a valid assumption?