RE: European Communities and Radiation Exposure of Flight

[Charles Willis <CAW@nrc.gov>]

	         -Reply

Good Morning Radsafers,

Sandy Perle asked about my comment on doses to members of the public.  I did not
intend to say anything new.  The 300 mrem annually from natural sources being the
average for the US population comes directly from the NCRP, specifically,
NCRP-94 (1987).  It consists of 100 mrem to the total body plus 200 mrem CEDE
from radon daughters.  (This same report attributes an additional 60 mrem to
man-made sources, essentially all medical exposure.)

The high doses are primarily from radon.  Long ago and far away, I was involved in
constructing what was intended as a low level counting room but which proved to
have such high levels of radon that occupancy had to be limit to avoid exceeding
the occupational exposure limits.  Such anecdotes abound and are so much a part of
the common knowledge that it would be difficult to publish such stories.  However,
Bill Dornsife and Ajit Bhattacharyya have written a paper (I do not know its
publication status) addressing these relatively high doses from natural sources
(among other things) and pointing out that, if our concern is about radiation dose,
we seem to be directing our regulatory attention to the trivial and ingnoring the
important sources. Radon is the principal source of dose (whether it does any harm
or not is another issue), but there as other potentially important sources such as
thorium; the DAC for thorium is a factor of 6 lower than the DAC for Pu-239, yet
thorium is widely used (e.g. in welding rods).  Clearly, we have no way of knowing
the actual maximum dose from natural sources but Dornsife reports a number of
homes with radon levels exceeding 100 pC/L, which presumably implies annual
doses exceeding 2,000 mrem CEDE.

These dose numbers are open to debate but the basic principle seems
well-founded; that is:

          Everything is radioactive and extending  regulatory control to
          too many sources could have a severe economic impact.

Charlie Willis
caw@nrc.gov