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I was searching a lot and could only find dosages for curing cancer and allowed emission, but no Iodine-131 dose that could be connected with increased thyroid cancer risk (like, 10mSv is the radiation dose resulting with measurable increase of cancer).

The Central Laboratory of Radiological Protection publishes Iodine-131 content in air measured in $\mu$Bq/m$^3$.

The number has grown by 3 orders of magnitude since the Fukushima accident, and while I strongly believe it's still good 6 orders of magnitude below dangerous levels, there's no convincing of some people without solid numbers - and finding these has proven quite hard.

So how can I then get either the safe levels of I-131 in air in ($\mu$Bq/m$^3$) , or a way to (indirectly - this gonna be convoluted) convert the content in air ($\mu$Bq/m$^3$) to dose equivalent radiation ($\mu$Sv) from absorbed Iodine?

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up vote 2 down vote accepted

It's difficult to get hard figures without exposing people and seeing how many die! Then the problem is that for low levels of exposure you have to workout how many extra people have died

The Nation Cancer Institute has some calculators and papers based on US nuclear testign exposure

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how is this an answer? It should be a comment. – user346 Apr 5 '11 at 13:43
Still, it provides lots of materials and conclusions, like direct absorption from air is insignificantly low (e.g. 0.004mrad vs 1.4 rad) comparing to ingestion in milk. Doses of order of 1mrad get absorbed by heavy milk drinkers for 1nCi/m^2 grazing grass contamination. Assuming a rain wipes a column of 10km of air clean of I-131 ions, depositing them on soil below, with ~2mBq/m^3 this contamination will result with roughly 20 microsieverts of equivalent dose for drinking the milk. Totally harmless. – SF. Apr 5 '11 at 14:42
@Deepak - there seemed to be lot of reports to download form the site but I haven't read them all – Martin Beckett Apr 5 '11 at 15:12

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