Current Tokyo radiation readings from personal geiger counters

"2011-04-16 7:22: 21 micro-Roentgens/h (~21 cpm). 0.218 micro-Sieverts/h. Location: Kita-ku, Tokyo. Weather: partly cloudy, winds from the south. Safe."

When obtaining a radiation reading, it's always helpful to consider that figure with a yearly time-frame in mind so you can properly gauge your maximum permissible dose.  In the case above, it's helpful to keep in mind:

• .218μSievert per hour yields an annual dose of 191 mrem
• Normal background levels in Tokyo prior to the Daichi incident were at 0.04μSv/h, so these readings  are still about 5x higher than usual
• The source contributing to these higher readings are not cosmic sources as they would be during air travel; they are from radioactive fission products that will enter the body and deposit themselves in bone, tissue
• The isotope breakdown in air is very difficult to ascertain, even when keeping track of released numbers from government agencies.  For example, how much Cs-137 contributes to the 5x reading vs Cs-134 or I-131

These doses are actually tolerable and probably wouldn't bump an adult above his/her recommended MPD,  but if i had a baby and kids, it would be quite disconcerting to continually expose them to radiation levels that have fission products as a primary source.  This is the exact trepidation with most Japanese who have relocated to areas with lower readings.

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