• Jacksonville, Florida


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.

The opinions expressed in this letter to the editor are the writer’s own and do not necessarily reflect the policies of The Japan Times.

jamee mikell

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