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 $ mpd@netcom.com $ via Finger. $