I'm curious about the math in the April 12 article "High radiation well past no-go zone: Greenpeace." It begins by describing an exposure rate of 4 microsieverts/hour, which it says amounts to 5 millisieverts/year. If that math is correct, reasonable comparisons would be a mammogram (3 millisieverts in a very short period of time) or a chest CT (5.8 millisieverts also in a short period of time). Both procedures would seem relatively benign since they are described as well below any risk threshold.
However, if I do a little math, 4 microsieverts/hour multiplied by 24 hours/day gives me 96 microsieverts/day. Multiply again by 365.25 days/year and I get 35 and a fraction millisieverts/year, quite different from the 5 millisieverts/year number cited.
My calculation assumes a constant rate of exposure. Maybe Greenpeace's numbers consider radioactive isotope decay that reduces exposure rates over time, which would also suggest that the long-term risk would quickly decline below the (innocuous) mammogram level.
So, I'm wondering (a) how Greenpeace arrived at the 5 millisieverts/year number; (b) if it really is 5 millisieverts/year, why should this spark panic and school closures (are exposure levels significantly less a few streets away where kids are living?); and (c) even if it is 35 millisieverts/year, that's still below the maximum permitted dose for U.S .radiation workers (50 millisieverts/year) - go to www.nrc.gov/about-nrc/radiation/health-effects/info.html.
Radiation exposure is something to be watching carefully and guarding against with appropriate medical vigilance, but maybe this disaster is not quite the Chernobyl scenario that Greenpeace has invoked.
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