This is a very important question which has been hotly debated in
recent years, due to the use of depleted uranium in ammunition fired in
recent wars. (Ordinary bullets are made of lead, but the military has
developed some special ammunition made of uranium. )
Depleted uranium is almost entirely made up of U238, which has a
much longer half-life than U235, and therefore the nuclei decay much
more slowly and emit much less radiation per pound of the stuff than
U235. U235 spontaneously decays fast enough to be useful in making
nuclear fuel for reactors or for weapons. Naturally-occurring uranium
is mostly U238, with a small amount of U235 mixed in. The U235 may be
separated out to make nuclear fuel, and the remaining U238 is a waste
product, which is mostly useless. It is a bit less radioactive than
natural uranium. It is dense, hard, and not too expensive, and so
putting U238 in ammunition instead of making bullets entirely out of
the much softer metal lead, sounds like a good idea if you want to make
bullets that can punch through armor.
U238 decays by emitting alpha particles (two protons and two
neutrons stuck together), and by spontaneous fission. Alpha particles
have a very limited range through air (a few millimeters), and do not
penetrate even very thin layers of most materials. Larger nuclear
fragments travel with even more difficulty. Handling bullets probably
isn't hazardous as long as direct contact is minimized, and as long as
grinding, dust, and powder is not made which could be ingested. Current
opinion from the European Union and the State Department is that the
radioctivity in depleted-uranium ammunition poses a negligible health
effect for soldiers using the ammunition as long as proper handling
procedures are followed. (But it is an active area of debate and
further reports can come out saying otherwise).
The people living around spent bullets may not be so fortunate.
The uranium in a bullet may vaporize and burn when it strikes an
armored vehicle, producing fine dusts of uranium and uranium compounds.
These are toxic (most heavy metals are poisonous), and can be ingested.
Alpha particles don't travel very far, but if the uranium is ingested
into someone's body, they don't have to travel anywhere to cause their
damage. It is a separate debate entirely if the residents of a country
where a war is fought with depleted uranium ammunition are at an
elevated health risk. Certainly the presence of depleted uranium will
not make anyone any healthier.
Tom (w. Mike)
(published on 10/22/2007)