Not to be nasty, but depleted uranium is not the hardest substance known. That remains, AFAIK, diamond.
The interesting thing about DU is that it is very dense, just like some noders. This makes it an excellent material for projectiles, because as we know:

Kinetic energy = 1/2 m * v2

Where v is velocity and m is mass. So, if you have a weapons system like a Vulcan machine gun and want to make it more powerful (more precisely: want more kinetic energy to be delivered on the target for every projectile), one way is to make the ammo DU.

An additional interesting property of DU is that it is pyrophoric, which means that small scraps of it burn. Thus when a DU shell enters a tank it ignites everything flammable. Including launch charges for the tank gun.
DU is not very radioactive, because all the radioactive stuff has been taken out of it (otherwise it would not be depleted, would it ?). It is just a material which happens to be a byproduct of uranium enrichment (for fission purposes), and to have desirable mechanical qualities (for a balistic weapon, of course).
A good substitute for DU is tungsten (wolframium), which happens to be more expensive for the US.
The health effects of exposure to DU are not clear yet.

Just to insert a few more facts:

First, uranium is relatively soft -- however, that doesn't matter when it's traveling at several Mach numbers.

Second, while it is one of the densest materials going, it's not the densest. That honor goes, depending on who you ask, to either iridium, or its neighbor on the periodic table, osmium. These are not used in tank shells for the following reasons: they are rare and expensive; they are extremely painful to machine; and they have very high melting points, making them difficult to cast.

Uranium is difficult to machine because it is pyrophoric, but it is within reason.

The critics of DU do have some points -- it is slightly radioactive and it does have heavy metal toxicity. As a result of public pressure and cost issues, the US Army has switched back to tungsten anti-tank projectiles, which are almost as effective and much cheaper. They use incendiary material at the base of the shell to replace depleted uranium's incendiary effects.

Depleted Uranium ammunition is most commonly used (by the U.S.) in two weapons: APFSDS tank gun ammo of 105 and 120 mm, and in the 30mm slugs fired by the GAU-8 30 mm cannon carried only by the A-10 Thunderbolt II ground-attack aircraft, more commonly known as the Warthog for its somewhat unlovely profile. (Actually, that's a matter of opinion; I think it looks damn cool, but then again, I'm a warmonger :-)).

Depleted uranium is very, very slightly radioactive. However, so is cigarette smoke (contains thorium, among other things) just to keep this in context. In addition, given that the main use of this stuff (in this application) is to break things and kill people, whether or not it leaves slightly radioactive (again, cigarette smoke-level, or less than an x-ray) remains about seems academic. The effluvia from a burning destroyed armored vehicle is far more dangerous to the environment and any nearby personnel than such remains might be. Burning plastic, aluminum, and rubber, not to mention all the nasty stuff used in modern electronics, plus an entire fuel load of diesel or turbine fuel, plus any ammunition the target tank was carrying, dwarfs the contamination of the DU.

If I was ever to be one of the guys who had to follow tanks into combat (tanks can't survive without infantry) I'd cheerfully accept the risks of toxics if it meant the tank I was walking next to had a better chance of killing the tanks across the way that wanted to kill me.

zeolite, regarding your writeup below, a couple of points. First of all, your assertion that the correlation between 'areas where DU was used' and the increase in 'illness and cancer' is a tad spurious. For one thing, 'places where DU was used' tends to have a high correlation with 'places where highly destructive weapons of various types were used, often extensively.'

The Gulf War saw many other forms of documented toxics release, from the U.N. forces destroying chemical weapons stocks to the deliberate contamination of enormous swaths of land and sea by the release and/or burning of thousands of tons of petroleum, a substance from which most of our daily carcinogens are originally extracted. Documented use of chemical weapons also occured in the region, before and after Desert Storm, when Saddam Hussein gassed rebellious villagers in his own country.

The Vieques range, while of course taking DU fire, was also used for years (and continues to be) for the testing of both conventional and rather exotic conventional explosive munitions - compounds of high complexity and, compared to an inert DU shell (inert in the explosive sense) of extremely high dispersal and distribution from their means of employment. Finally, Kosovo has spent several years enduring the use of tons and tons of conventional weapons, the aerosoling of nasty stuff ranging from concrete and asbestos (silicosis, anyone?) to gasoline and diesel (petrochemical toxics).

In sum, these three environments also have an extremely high level of other contaminants, many of which have been documented to produce some of the same symptoms as radiation sickness (the lighter petrochemicals can cause loss of hair, nausea, and body chemistry disorders as well as cancer, for example). While I don't wish to claim that DU cannot be the culprit, I would very much like to see the reports you mention (references?) so that I might evaluate them for myself.

Just a few more points to help flesh out this set of DU writeups:

Depleted Uranium has a density which is about twice that of lead.

As stated previously, DU is slightly radioactive, emitting low levels of alpha particles. Since these don't travel very far in air, the greatest health risk is caused by inhalation or ingestion of DU particles created when DU armour is hit or when a DU-tipped artillery shell explodes.

To put the radiation level of this material in perspective: The radiation level is around 30 million times less than that of the americium used in household smoke detectors. Of course, we are not likely to ingest americium particles from our smoke detectors, so they don't pose a significant health hazard.

The predominant influence on the health of people exposed to DU dust is caused by its chemical toxicity. The amount of DU particles ingested which can lead to heavy metal toxicity problems is thousands of times less than that required to cause radiological problems.

Use of Depleted Uranium on the battlefield is suspected of being the cause of Gulf War Syndrome.

Most of my evidence for this writeup comes from a Washington Post article by David Brown, dated January 28, 2001, entitled "Risks from Uranium Limited, Experts Say." It was buried on page 20. I won't burden you with the whole cut-and-paste text, because you can look it up yourself if you really want to.

  • Long-term exposure to natural uranium (which is more radioactive than depleted uranium) doesn't affect one's risk of leukemia or lung cancer; several medical studies are quoted. The implication is that depleted uranium, which is less radioactive, is even less likely to cause such problems.
  • Of the 60 people with DU shell fragments in their skin and bones from the Gulf War, none have developed leukemia or any other kind of cancer, and they have fathered 38 children collectively. That was ten years ago; if they're still healthy, this Balkans Syndrome (or BS, as I like to call it) is just a media fairy tale.
  • Since 1940, a dozen studies following 78,000 people working in uranium mills (where uranium dust is in the air constantly) have been published, and none has found an increase in cancer or other serious illness. The exposure level of these workers is much higher than anything that would occur in the Balkans.
  • People with exposure to alpha particle-emitting isotopes show no overall increase in leukemia, the disease which DU reportedly caused in the Balkans. The best evidence is a study of women who painted radium on luminous watch dials in the 1920's: they had huge increases in other cancers, but no excess leukemia, because alpha particles simply can't get through bone to the marrow, where leukemia starts.

Also, a few more facts regarding the composition and density of DU: it's mostly U-238, which is the least radioactive isotope of uranium. U-235 and U-234, the highly radioactive ones, are used for reactor fuel, and are less dense than U-238; there is a performance incentive to make DU as radioactively inert as possible, because this increases its density.

If you really want to know why Spain, Italy, and the Netherlands are protesting the use of DU munitions, look at which countries proposed and supported (strongly) a European Rapid Reaction Force--NATO without America, Canada, or Great Britain--at the time of the first DU articles. The DU scare may just be politicized hype. It could be that it's designed to demonize America, and divide NATO along a very carefully thought-out line. Countries with a vested interest in removing American influence from Europe are likely to support and amplify this rumour; countries who don't believe it have no choice but to keep quiet for months while performing medical studies. You don't need proof to go to press with a story that says "possible," but you do need proof if you say "improbable." It's an easy trap to set; by the time we've proven depleted uranium is mostly harmless, nobody will care. Well, it hasn't been proven, but it looks more and more like depleted uranium is basically incapable of causing leukemia outbreaks.

It helps to remember that the media make money when they sell papers or hook viewers. Stories about things being found "harmless" aren't nearly as riveting as those that promise to tell you "the truth about what common household item could kill you -- next!" Uranium is a scary word because it implies that harmful radiation is present. As long as you differentiate between claims that "it's uranium: how can it NOT be bad?" and claims that it is a potentially harmful heavy metal, you'll be on your way to understanding the truth about DU.

To sum up: I wouldn't let your kids go chewing on the stuff. Depleted uranium is still uranium (a heavy metal) and probably is at least as bad for you as lead when ingested.

By the way, if you're downvoting me for style, please drop me a message. You're in the minority, but this node is meant to persuade everyone, and if the style doesn't work, I'd like to know so I can fix it. If you're downvoting because the word uranium scares you and you refuse to believe that DU is not as harmful as it's portrayed to be, way to be objective about it.
While the U.S. government keeps claiming that depleted uranium is harmless, there is a definite link between its use and then immediate surges in serious illnesses and cancers in the area it was used. The three prime examples are the Gulf War, Kosovo, and the small island of Vieques to the south of Puerto Rico; which the U.S. has turned most of into a practice range for various military exercises.

The Pentagon bases the claim that DU is harmless because it is only mildy radioactive. This may be true, but until there are more independent studies we can't be sure. To give them the benefit of the doubt, let's assume that it's true, that DU is mostly harmless on its own. Okay, good. Now, how can the link between its use and then the sudden rise in serious illness and cancers be explained? The most logical thing to do is to go back and look at where the DU was produced. The three main nuclear powerplants which produced DU back in the 1980s were in Paducah, Kentucky; Portsmouth, Ohio; and Oak Ridge, Tennessee.

These powerplants are important because it's where other nuclear weapons products were produced. So they were, without a doubt, contaminated with other nasty radioactive materials. The U.S. Department of Energy confirmed this when they found the machinery that was used to make DU was contaminated with such things as neptunium, plutonium, and technetium-99. Now, plutonium is one of the worst radioactive materials that is used. If very special procedures are not taken while handling it, the people doing the handling will get some nasty things (i.e. cancer). Not surprisingly, that's exactly what happened; especially at the Peducah, Kentucky plant.

That plant was designed to handle uranium, not other such things as plutonium. But, it was indeed found to have been contaminated with plutonium, among others. There's a very interesting link at this point. Thousands (yes, thousands) of people who worked at the Peducah plant while producing DU (who knows what else, Uncle Sam probably) became seriously ill; which is to say they suffered from cancer, early death, etc. These symptoms are exactly the kind that are found in Gulf War veterans who suffer from Gulf War Syndrome and also Iraqi people who live near where DU was used. They are also the symptoms found in people and soldiers in Kosovo and the residents of the island of Vieques.

A recent test (1999) on the DU weapons stores by the U.S. government itself showed that the stores contained plutonium and other nuclear material which was not DU. And the United Nations, which is investigating the Balkan War Syndrome, issued in January, 2001 a report that it found elements indicative of plutonium in Kosovo.

Studies in Vieques show that the bombing ranges are also contaminated with DU. The U.S. Navy admits that it did indeed use DU weapons on Vieques, but that it was an "accident" because they loaded the wrong munitions onto the attack aircraft for the training exercises. The only reason the Navy even admitted this is because campaigners on the island forced them to through the Freedom of Information Act. The investigation showed that many, many areas of the island were contaminated, which could only be the result of systematic exercises where DU was being used with full knowledge for at least a decade. One "accidental" use of DU wouldn't be able to produce the effects which now exist on the island. 9,000 residents live on Vieques, and more than 1/3 of them are suffering from the symptoms associated with radiation poisoning. 3,600 of the residents are planning to bring a class action lawsuit against the government.

When you add all of this up, it makes a pretty strong case that DU being used by the U.S. is not harmless, but rather malicious. I think European countries that want DU banned are hardly doing it to "demonize" America and divide NATO (as Jurph's writeup states above).

As someone who was in a situation where large volumes of DU rounds were fired (pre-Gulf War in Operation Praying Mantis), I can tell you a few interesting things about this nifty metal.

First off, if you can hold a DU round in your hand, you'll be able to tell how much heavier it is in comparison to regular lead. DU rounds are used in the US Navy Phalanx anti-missile systems, spewing 3000 rounds/minute. These bullets have a very high kinetic energy when they are fired, and they penetrate incoming missiles rather well, either detonating them or damaging their guidance systems enough so they miss the target.

They are not very radioactive in a relative sense. One idiot I knew of had snagged a live DU round and was carrying it around in his coverall packets. Alpha radiation is not strong enough to penetrate bones, but having it two inches from your testes is not what I consider a Nobel prize winning move. It just so happens that he ended up with testicular cancer less than a year later. Coincidence? Perhaps, maybe it was there already. Enough to make me wary, anyway. Any exposure to something that is radioactive or has a toxic heavy metal problem is something to be avoided by sane humans. The helicopters I worked on had a device that used a beryllium cable. Safety regulations kept you from handling it too much, and not to check for broken strands with your hands, since you could get a splinter, then get blood poisoning or cancer from it. Again, something to be avoided.

As far as the DU rounds, when they're fired off by something like the Phalanx, part of the round is subjected to very high heat and pressure. This gives off some dust, especially from the wadding and the gunsmoke cloud that bellows from the gun. While it may be harmless in relation to other carcinogenic items, it still remains a nasty, toxic and radioactive cloud of crap that you do not want near your living tissues.

Since "Europeans" are used as ammunition in some of the writeups, I'd like to add a comment from the European angle:

The discussion about use of depleted uranium in Kosovo was indeed a scare, but I would't think it was designed to discredit the U.S. as Jurph would have it. Interesting conspiracy theories aside: can you think of a speculative journalist who wouldn't sell his mother to get his hands on a story like this:

"Secret Uranium Weapons Used Among Women And Children"

The imagined target reader/viewer for those journalists wouldn't know uranium from peanut butter, but they all agree that it sounds scary.

So what happended?

  1. Big headlines.
  2. Uninformed populistic politicians sense a chance for some prime time media coverage and appears quivering with righteous indignation demanding investigations and a ban on depleted uranium everywhere
  3. Informed but not so populistic scientists appear and tell everyone not to be worried in a way that makes people even more worried
  4. Media gets bored and finds another scandal, royal wedding or revolutionary new diet to put on their front pages.

In the wake of this pointless (and not very original) excercise, some investigations were actually made. One of them recently published in Sweden probably killed the discussion there for some time: Urine samples taken from Swedish KFOR (and UNPROFOR) soldiers showed less uranium traces than samples from soldiers who had stayed in Sweden during the same period of time. Explanation: The uranium content of Swedish soil is higher than that in Kosovo and if the KFOR soldiers had been exposed to uranium from DU shells, it would still be less than what they would get back home.

I don't claim to speak for all Europeans and would warn against thinking of Europeans as a homogenous group...
Depleted Uranium a comment from Ireland

During the NATO bombing of Kosovo top army officials and spokespersons assured us that there would be no lasting environmental damage. The weaponry was supposed to be 'smart', hi-tech and clean. But now there is growing evidence of the permanent harm done by the use of depleted uranium munitions.

NATO officials recently (2001) admitted that their aircraft fired more than 10,000 depleted uranium missiles in Bosnia between 1994 and 1995 and that they fired them on 112 sites in Kosovo in 1999. A UN survey has found evidence of "considerable contamination" by radioactivity at 8 of 11 sites hit by depleted uranium weapons in Kosovo. Another UN report in May warned that much of Kosovo's water could be considered unfit to drink.

Six Italian soldiers who served in the region have contracted leukemia and died. In Belgium, five cases of cancer have been diagnosed in soldiers who served in the Balkans. Several cases of leukemia have developed among Dutch soldiers and Spanish military personal are to undergo a check. Irish personnel currently stationed in the region have been told not to drink the local water or eat locally produced food.

In the space of just a day the Irish Defence Forces did a u-turn on the issue and have announced that all personnel who were in the region will be screened for cancer. But they have not joined the calls from other European countries for a ban on depleted uranium weapons and a full enquiry.

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