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areas where annual radiation measurements are below 20 millisieverts
per year, a government safety guideline, residents will have free access
to their homes during the day and will be allowed to return permanently
at the earliest opportunity post-decontamination. Where readings are
between 20 to 50 millisieverts annually, evacuees will also have
unrestricted access during the day although their permanent return will
come later. In areas where measurements top 50 millisieverts, residents
will not have free access and they will not be allowed to return for a
minimum of five years.
A past BNC guest poster, engineer Chris Uhlik,
analysed the situation a private email distribution list, and I thought
his summary with respect to LNT (linear no-threshold hypothesis of
radiation damage to living organisms) was very useful. With Chris'
permission, I reproduce it below:
official position of every regulatory agency & scientific body, and
even the people who will tell you "we don't know what's going on under
50 mSv", the weight of the evidence favors LNT.
Here's what I think is going on:
50mSv/year we can't find any epidemiological data to support LNT. There
is simply too much noise and other effects to see sub-0.5% changes in
cancer rates in populations where the variations from other effects
(smoking, stress, chemical exposures, etc) are in the range of 20--45%.
rates of different kinds of cancers are affected differently by
radiation. Some kinds appear to increase while others decrease. Some
kinds of cancer are more treatable than others and thus result in
different mortality rates, even if the occurrence rate increases. Simple
statements like "cancer death rates show a LNT response to radiation
exposure" are way too simplistic to be true, but such statements are
easy to base regulations around. When regulators feel a need to support a
regulation with some math, they'd rather choose simple math than
more-correct, but difficult to understand and explain math.