|Shinjuku Station, Tokyo Photo credit: the blogger|
I discovered that the Japanese Ministry of Economy, Trade and Industry puts out a daily pdf giving the radiation rates in micro-Sieverts per hour by prefecture.
Below I paste in their release for April 21, 2011. The box to the left center gives comparison values of (1) the average radiation in micro-Sieverts that most people everywhere are exposed to in one year's time, (2) the dose received in a normal chest x ray, and (3) the added cosmic ray dose you'd receive on a round trip from New York to Tokyo and back.
So if you were at Shinjuku Station for an hour yesterday, you would have received 0.072 micro-Seiverts. And if you were to stay there for an entire year with no change in dose rate, you'd receive 630 micro-Sieverts, actually less than your typical annual dose from all sources of about 3,000 micro-Sieverts (which might include for example 70, 400, 600, and 2,000 micro-Sieverts per year due respectively to (a) living or working in a concrete building, (b) decay of natural radioactive Potassium-40 in your bones, (c) radioisotopes left over from the atomic bombing of Hiroshima and Nagasaki and subsequent A-bomb tests, and (d) the Radon-222 you might breathe if you spend much time in a basement or mine).
If you lived in Fukushima Precinct (presumably outside the evacuation zone) yesterday you'd have been receiving 1.75 micro-Sieverts per hour, and you would accumulate 15,330 micro-Sieverts if you stayed there for a year and nothing changed. By comparison, the maximum yearly dose allowed for U.S. workers in radiation environments is 50,000 micro-Sieverts. Here is a handy chart in case you'd like to look up some of these numbers yourself.
Now all you have to do now is to realize that the fallout in the U.S. is undoubtedly diluted 10 to 1,000 times compared to Fukushima Prefecture. So put away your potassium iodide pills.