From Steuart Campbell
It is usual to express average exposure to radiation in millisieverts per
year, not milligrays per year as in your story. The former takes into account
the effects of different types of radiation. The average total dose most people
are exposed to is about 2.2 millisieverts per year, which would only be the same
in milligrays per year if all the radiation were beta and gamma rays.
The sources you list for this radiation are strangely selected. Ground
sources constitute only 14 per cent, while the nuclear industry accounts for
less that 0.1 per cent (and atmospheric bomb tests only 0.4 per cent). Medical
X-rays account for about 12 per cent (not up to 50 per cent as you claim). But
why not mention that nearly half comes from radon and thoron in our homes, or
that 10 per cent is derived from cosmic rays?
Edinburgh
