background vs. reactor

[Michael Stabin <stabin@npd.ufpe.br>]

First, if I may, I'd like to say how encouraged I am by the recent level of
dialogue on the list.  Where we may have stumbled a bit in weeks past, I
think we are redeeming ourselves recently. It helps that Norm's tone is more
reasonable than that of our lawyer friend from Florida, but, as Melissa
pointed out, it takes two sides to maintain a flame war, and I think that
recently the level of self-restraint on both "sides" has been commendable
(except for
a couple of recent flames - Franz, may I suggest that Norm didn't talk with
you
by private e-mail perhaps because you are often so harsh with people.  Norm,
please
keep posting).

Regarding Norm's post on the background vs. reactor nuclide theory (sorry
this
is a bit late, I can't post from home over the weekends), I think
the short-lived/long-lived argument is not completely absurd on its face -
at least as regards *internal emitters*.  I think what they are getting at
is the effect of dose rate on the dose delivered and the causation of
subsequent effects, if any.  As regards external dose, I don't see that it
would have an
influence - the radiation field has such a great mixture of energies and
sources that the effects of any particular nuclide could not be perceived
biologically.  But if one inhales or ingests a given activity of a
short-lived nuclide and receives a dose of X, and one receives the same dose
X from a longer-lived nuclide in the body, one *might* suggest a difference
in effect due to the difference in the dose rate with which the dose was
delivered. (OTOH, the dose from intake of Y Bq of a short-lived emitter will
be less than the dose from an intake of Y Bq of a longer-lived nuclide, more
or less in proportion to the effective half-time within the body, which is
related (in a nonlinear fashion) to the nuclide physical half-life). The use
of a dose
rate effectiveness factor in radiation risk assessment does reflect current
thinking of a number of well recognized international bodies.

However, this effect, if present, is negated by the fact that, as correctly
noted by other contributors, that "natural" background is comprised by both
long-lived and short-lived nuclides, as well as by those which disperse
relatively uniformly throughout the body (K-40, Cs-137), and those which
concentrate in certain organs when taken into the body (Rn-222 and progeny,
Ra-226, U-238 , etc.).  The "new/old species" argument is interesting, but
not very credible to me, unless we are discussing a chemical rather than a
radiological effect. Reactors do expose people to low levels of some
emitters that are not in the natural background mix, but from the cell's
"point of view", a microGy is a microGy (not inclusive of the possible dose
rate effect), whether it is from Xe-133 or K-40.  And nuclear medicine,
which emerged in roughly the same time frame, also exposes the public
internally to various "new" nuclides and chemical compounds, and accounting
for this effect in populations near power plants will be problematic, should
it even exist, which I find doubtful.

So I think that the point of view that this is "apples and oranges" is
off-base, as has been objectively shown.  And I agree that the scientific
basis of the TF project (if the basis has been faithfully communicated in
the transferred e-mail), when confronted by the "Denver" effect, does not
hold water.


> > Simple answer: comparing background vs. reactor emissions is apples vs.
> > oranges.
> >
> > Background
> > - is made up of mostly long-lived products
> > - generally disperses throughout soft tissues
> > - is something that humans have become accustomed to over millions of
years.
> >
> > Reactor emissions
> > - is made up of both long-lived AND short-lived products
> > - does different things to the body (attacks thyroid cells, attacks
bone/bone
> > marrow cells)
> > - is very new, only since 1945
> >
> > Thus, health effects of each will be different.


Michael Stabin
Departamento de Energia Nuclear/UFPE
Av. Prof. Luiz Freire, 1000 - Cidade Universitaria
CEP 50740 - 540
Recife - PE
Brazil
Phone 55-81-271-8251 or 8252 or 8253
Fax  55-81-271-8250
E-mail stabin@npd.ufpe.br

"Quantum Mechanics: The dreams stuff is made of"
- Steven Wright


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