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From: stiatl!john@gatech.edu (John DeArmond)
Newsgroups: sci.military
Subject: Re: Shielding Nukes
Message-ID: <8629@cbnews.ATT.COM>
Date: 27 Jul 89 11:30:51 GMT
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From: stiatl!john@gatech.edu (John DeArmond)


This discussion regarding radiation hazards and detectability of nukes
is getting a bit out of hand.  Being a health-physicist by training
and having worked on some projects in this area, I want to try to add
some fact to the fiction being bantered about.  Some of the details will
be sketchy, as some of my work was classified and I really don't want to
make fine line distinctions here.

The 4 major constituents of a bomb are U-235, U-238, Pu, and 
H-3 (tritium).  Tritium emits a weak beta with insufficient energy
to escape its matrix/solution.  Thus the radiation may only be detected
by in-situ detectors.  Unless ingested in LARGE quantities, H-3 is harmless.
Plutonium in its refined state emits an alpha which has a range in air of
about 3 inches.  Daughter products emit a variety of radiations, some
energetic enough to be detected.  Uranium and its ever-present daughter
products emit all 4 emissions (alpha, beta, gamma & neutrons).

Plutonium and Uranium are both low specific activity isotopes which means that
a given mass emits relatively low radiation levels.  In real terms, 
Uraninum metal may be handled with relative inpunity as it presents essentially
no hazard.  Plutoninum's chemical toxicity greatly outweighs its radiological
hazard.  Working levels (permissible human exposure) are measured in micrograms.
Plutoninum is only a hazard if ingested.  The radiation emitted 
external to the body is harmless.

In practical terms, a warhead presents no radiation hazards to people (un-
detonated, of course).  Depending on the configuration, there may be some
sensible heat on the surface of the weapon.

In terms of detection, technology exists to detect Special Nuclear Materials
(SNM) at great distance.  This technology involves large volume detectors,
gamma spectroscopy, active shielding, and computer analysis.  This equipment
can recognize the unique gamma signatures emitted by SNM.   I have worked
with helicoptor-mounted equipment that is used to sweep a large area.
One instrument I worked with was tested by being able to locate a kg of 
Pu oxide suspended in a 100 foot deep well.

For those wanting more information, consult the public literature on
the Nuclear Emergency Response Team (NEST).  If you REALLY want to 
find out how well these fellows do their jobs, just acquire a kg of Pu and
sit tight.  They'll find you soon enough :-)
-- 
John De Armond, WD4OQC                     | Manual? ... What manual ?!? 
Sales Technologies, Inc.    Atlanta, GA    | This is Unix, My son, You 
...!gatech!stiatl!john    **I am the NRA** | just GOTTA Know!!!