![[logo]](Tutorial.jpg)
| IDUST TUTORIAL CENTER |
 Home Page |
 Facts On DU |
 Radia- tion |
 Internat'l Law |
Click HERE to contact IDUST. |
Depleted Uranium (DU) is the radioactive waste product that remains after Enriched Uranium has been removed from natural uranium metal. It is used by the military in many countries as armor-piercing projectiles, as ammunition, and as tank armor. It is also used as ballast in aircraft controls and in oil drilling equipment. In fact, DU is finding its way into the commercial marketplace in a variety of surprising and troubling venues.
Uranium ore, like most metal ores, must be refined after it is mined from the ground to produce pure natural uranium metal. This purified metal contains three isotopes, or nuclear forms, of uranium, designated by their atomic mass numbers. These three isotopes are U-234, U-235, and U-238. All three are radioactive. There is only a trace of U-234. Most of the natural uranium metal is U-238, amounting to 99.3% of the metal, while U-235 accounts for the remaining 0.7%.
It is only the U-235, however, that has properties useful for nuclear energy reactors and atomic and hydrogen bombs. And to do its job, it must be present in much higher concentration than 0.7%! A nuclear reactor requires at least 5% U-235, while an atomic bomb requires enrichment to as much as 90%. So a very expensive and complex process called "enrichment" takes place to increase the concentration of U-235 and produce "enriched uranium".
What is left behind is "depleted uranium", or DU, which now is 99.8% U-238, with only 0.2% U-235 left. It has a density of 19.05 grams/cc, nearly 1.7 times as dense as lead. It is also a pyrophoric metal, which means that, like magnesium, it will burn in air, producing a "smoke" of very fine aerosol particles of uranium oxides that are small enough (less than 10 microns in diameter) to be inhaled and to become lodged deep in the lungs where they can remain for decades.
It is the combination of high density and flammability that make DU such a coveted weapon by the military. When a DU projectile hits a tank, the much less dense steel armor gives way. At the same time, the impact causes the DU to ignite, turning it into the equivalent of a welding torch. The projectile quite literally burns its way completely through the tank wall. Inside the tank, it sprays molten uranium on the occupants, burning them alive, and often has enough momentum to burn another hole through the opposite wall. Usually the burning projectile will ignite the ammunition or the fuel within the tank, causing it to explode catastrophically. It is not difficult to imagine why the military would do everything in its power to keep such a weapon from being banned!
U-238 has a radioactive half-life of 4.51 billion years. To understand what this means, you need to know a little about radioactive decay processes. A radioactive substance is unstable. The nuclei at the center of its atoms restructure themselves over time to achieve a more stable arrangement. This restructuring has two consequences. The first is that a small particle blasts its way out of the nucleus at nearly the speed of light. This is the "radiation" that we talk about. The second consequence is that the atom, having given up some of its nuclear matter, is transformed into a different substance! Physicists refer to the new substance as a "decay product".
This nuclear restructuring takes place over a sometimes very long period of time, as with U-238. In 4.51 billion years, the half-life for U-238, half of the atoms of U-238 in a given mass will have decayed into thorium-234. In another 4.51 billion years, half of the remaining mass will have undergone a similar decay. But even after these two half-lives, you still have 25% of the original mass of U-238 left! After a third half-life, you still have 12.5% left, and so on.
What makes matters worse, the decay products are often themselves radioactive with their own half-lives. For example, the thorium-234 produced when U-238 decays is radioactive, with a half life of only 24.1 days, and it decays to form protactinium-234 which has a 6.75 hour half life, decaying into U-234 which has a very long half life of 24 million years. In fact, there are 14 decay steps from U-238 before arriving at a stable non-radioactive isotope, lead-206.
Why is all this important to know? When you are talking about radiation from depleted uranium, U-238, you must also take into account radiation from thorium-234 and protactinium-234. U-238 decays by emitting an alpha particle, while both thorium-234 and protactinium-234 each decay be emitting a beta particle.
There are four common types of radiation from radioactive elements. They are:
For a description of radiation exposure and its effects on the human organism, check out my paper in the Radiation Section of this website.
Finally, if beta radiation from thorium and protactinium were not enough additional radiation burden from depleted uranium, there is one other extremely disturbing fact which was admitted by the US Department of Energy only in 2000. That fact is that the depleted uranium that is being used in all the applications mentioned above, has been seriously contaminated with radioactive wastes from nuclear reactors. This not only means that a sample of contaminated depleted uranium is much more radioactive than it would be if it were pure DU, some of the contaminants, such as plutonium, neptunium, americium and other trans-uranium elements, have a significant chemical toxicity of their own.