From: dpe@inel.gov (Don Palmrose)
Subject: Re: Notch another one up for the Greennazis
Organization: INEL EG&G Idaho
Date: Mon, 14 Dec 92 15:45:01 GMT

In article <51620@seismo.CSS.GOV>, stead@skadi.CSS.GOV (Richard Stead) writes:
> 
> 
> I still disagree that U is more toxic than Pu or that microCuries are useful
> in measuring toxicity of substances.  I will agree they are useful for
> measuring exposure.  Body burdens due to radiological effects are not that
> much different between a wide variety of isotopes when measured in terms
> of microcuries.  Basically, a microcurie of one alpha emitter in the body
> is as bad as a microcurie of any other, in particular if it remains in the
> body and preferentially irradiates cancer-prone tissues.  So the differences
> in terms of microcuries only shows up when a microcurie of a particular
> isotope is a big mass (due to long half-life) and the element has another
> toxic effect that is significant at less than that mass.  Toxicity of a
> substance is based on its mass, not its microcuries.

I thought in my last posting, I did the calculation that showed that based
on the body burden limit U-238 may have a lower limit based on the microCurie
unit, but based on mass, that it took less Pu to exceed the limit?  Thus
conceeding that point and even joked about it by comparing your errors to 
mine (2 to 1 remember).

> 
> Then surely you can see that a fraction of a microgram is far smaller than
> "extremely small".  Those common beam-balances found in student chem labs
> can measure 15 mg.  I have used balances supposedly accurate to a
> microgram, but certainly never a fraction of a microgram.  and 15 mg is
> not "a little bit of dust", you can make a satisfactory little pile out
> of 15 mg of most powdered reagents.  one milligram would be nearly a
> cube 1 mm square (water is exactly that, and the densest materials like
> iridium would be 1/20th of that volume, or 3/8 a mm on a side (about the
> size of a medium sand grain).  Now imagine 15 mg of a typical oxide
> (about 4 times as dense as water).  It's a more like pea-gravel, about
> 1.6 mm on a side.  As a powder, it would form a cone more than twice
> that big.  That's not a bit of dust.  I don't want others to think 15 mg
> of Uranium is small, becuase it isn't - you would be fully aware of an
> exposure that large, so no one need fear Uranium.
> 

Bottom line:  one does need to fear uranium if one works with it.

Again, we have a difference of perspective.  What you say above for the most
part, I do not doubt.  But to say that something 1.6 mm square or a powder 
that is twice as big is large enough to be noticable by someone exposed to 
that amount is not correct.  From my experience, such quantities can be easily
digested or inhaled in a day by an unranium worker without their knowledge if 
the proper precautions are not taken.  Accidents could cause that amount to be
easily exceeded also.

Powders are especially troublesome.  They are easily scattered.  From my 
navy days, we would sometimes use a powder that one can see with a uv-light
to simulate a radioactive-powder spill (we never had a problem in this area
because we worked very hard to prevent accidents before they happened).  If 
the people were not careful, you would be picking up the powder all over the 
place (hands, faces, clothes, etc.).  It quickly got people's attention.

Thus, when handling uranium, I would be careful with it (especially if it
is in a powdered form) because it is dangerous and I would want to minimize
my exposure to as low as practable.

I found it extremely interesting that the workers who built the first fission
reactor fifty years ago would handle the natural uranium with their bare 
hands and without face filters or resperators.  They even made some uranium
dice and rolled them down the concrete hallway watching the sparks flying
everywhere.

> > My last comment is that somewhere you mentioned that U is chemically dangerous
> > while Pu is radioactivity dangerous and imply that this makes a difference.
> 
> Only if you want to compare exposure in terms of microCuries.
> 

Again, they are both dangerous, whether their path is through chemical
interactions or through damage by radiation and both need to be treated with
a healthy dose of respect.

> 
> --
> Richard Stead
> Center for Seismic Studies
> Arlington, VA
> stead@seismo.css.gov
> 
> 

Don Palmrose





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