Re: radsafe posts

[David Scherer <scherer@uiuc.edu>]

I did not intend to continue this thread, but I feel compelled to answer a
public response to a private e-mail message:

>As before: no problem for "safety factors". But they don't change the units
>nor pretend to be scientifically valid, as q (wR) do. 

It has always been acknowledged that the Q value is the result of judgement,
not a unique physical constant as the compressive strength of a given
material.  Competent HPs understand their limitations and use them for
protection purposes, not for predicting actual biological outcomes.

>Not true. Thousands of experiments carefully measuring to destruction the
>compressive strength of many concretes and physical conditions go into
>establishing scientifically valid values that get written into engineering
>codes, to which are applied "safety factors" (that do not pretend to reflect
>physical reality). The lack of equivalent research in rad science is the
>direct result of failing to find similar responses. See the research with mice 
>populations exposed at a low dose range of 0.11 r/day in which they lived
>longer and were healthier. Research policy ignored the data and failed to
>follow recommendations of many true scientists who recommended more definitive 
>studies. 

My point is that we do not measure radiation effects directly, as we do
material properties.  And when we do attempt to measure radiation effects,
we sometimes include our safety factors that were originally intended for
protection purposes only.  This misuse of the DE is an error of the research
design and/or analysis, not of the definition for protection purposes.
(BTW, it is also an error of the analysis that predicts 1/4 of lung cancers
are caused by radon.  The Q=20 and tissue weighting factors used in these
predictions seem more speculative than the LNT model for beta/gamma radiation.)

My engineering example was an analogy, not a suggestion for concrete
testing.  Material properties are not tested by looking at crumbling
bridges, but this is how we look for radiation effects.  This is due to the
complexity of biological systems and ethical considerations.  We can test
concrete destructively; we cannot do so with humans.  We have to rely on
exposures resulting from accidents or other uncontrolled origins.  Despite
this we have a good body of knowledge about radition effects.  We have a
good understanding of acute radiation effects at high doses.  (This is
analogous to destructive testing of concrete.)  We do not know precisely the
effects of low doses over long time periods.  There are conflicting results.
(I know you think the results unequivocally show no effect, but I believe
they are unclear.)  Similarly, we do not know precisely how stresses below
the destructive limit affect the service life of concrete.  We cannot simply
rebuild a biological system (person), so the NCRP et al have decided to take
a more conservative approach than we use for structures.

As far as the rest goes, I do not agree with you that the ICRP, NCRP, and
government HPs have pursued a conspiracy.  But you might be able to sell it
to Oliver Stone or the militias.

Regards,
Dave Scherer
scherer@uiuc.edu