Radiation reached around 20 times normal levels in the capital Tuesday morning, the Tokyo Metropolitan Government said, while offering the assurance this reading posed no immediate risk to human health and that the public should remain calm. Japan Times
The National Academy of Sciences says there is no safe radiation dose: “that it is unlikely that a threshold exists for the induction of cancers..." BEIR VII, 2005.
Also check our radiation resources section for more information on radiation dangers.