Re: Nuclear Weapons Material

[mpd@netcom.com (Mike Duvos)]

Jim Dixon <jdd@aiki.demon.co.uk> writes:

 > I was told by what I considered to be reliable sources that
 > plutonium was extremely toxic.  Upon reflection, I am sure
 > that this is the word that was used: toxic, not radioactive.

Plutonium-239 emits alpha particles, which are helium nuclei, at
an energy of approximately 5 MeV.  Such particles are bulky and
can be stopped by a few centimeters of air, or a thin piece of
paper or metal foil.

In order to cause damage, alpha emitters like plutonium must come
in intimate contact with a material, such as the tissues of your
lungs or bones or the inside of your favorite memory chip.  A
billionth of a gram of plutonium inhaled or swallowed is
something to seriously worry about, but you can hold a lump of
the stuff in your hand as long as it is covered with a leakproof
cladding or vitrified into a ceramic.

It is in this sense that plutonium is extremely toxic and
hazardous to the environment, while at the same time not being
particularly radioactive.  Heavy shielding is not required
between you and it.

Of course once fissionable fuels are irradiated, they become
extremely radioactive due to a wide spectrum of short-lived
fission byproducts and then require precautions when they are
handled.

 > By "clad", do you mean coated in lead?

No - the desired properties of cladding are resistance to
corrosion and heat, as well as a low absorption cross section for
thermal neutrons.  We're talking about materials like zirconium
and iridium here, as well as specialized alloys of stainless
steel.

-- 
     Mike Duvos         $    PGP 2.6 Public Key available     $
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