Radiation and Its Danger to Human Beings

Here is a link to a very well written article by Eric Johnston of The Japan Times about radiation levels and their effect on human beings.

http://search.japantimes.co.jp/mail/nn20110316a4.html

Among other data, he reports that, as a kind of reference, a CAT scan exposes a person to 10 doses of what are called millisieverts.

The risk of radiation induced cancer rises from around 200 doses. The levels near the damaged reactors are in that neighborhood or higher. The levels in Tokyo are relatively low.

The point is, no one knows for sure. If you don't need to be in Japan, it may be wiser to stay away until the situation has been thoroughly dealt with. The wind could change, it might rain, the reactors could spew at a heavier rate than at present. No one can know until it happens.