My understanding is that normally natural uranium is not breathed into the lungs as it is bound into soil and rocks etc, but the dangers of DU in weapons is that when the warhead hits the target it burns and/or explodes which creates millions of tiny radioactive particles of urnaim oxide which can be suspended in the air and then sucked into and become lodged in the lungs. From the lungs these tiny radioactive particles pass the lung/blood barrier and enter the bloodsream and from there enter the internal organs and become stored in the bone.
While pure depleted uranium (U 238)puts out alpha radiation which is easily blocked by clothing or even the layers of dead cells on the surface of the skin, once inside the lungs or other body tissue the alpha particles do have the ability to cause damage to the cells and DNA. In addition, the radioactive decay process of U-238 creates two daughter elements, thorium Th-234 and protactinuium Pa-234 which both emit beta radiation (along with some gama as well) which is more powerful and more destructive than the alpha radiation,especially when the radiation is being emitted from radioactive material stored inside the body and not coming from external sources.
For more details see this paper by a nuclear physicist Leonard A. Dietz (recently deceased).
Contamination of Persian Gulf War Veterans and Others by Depleted Uraniumby Leonard A. Dietz
July 19, 1996 (last updated Feb. 21, 1999)
<snip>
After 25 weeks, Th-234 and Pa-234 have reached 99.4% of the decay rate of U-238 and for practical purposes have reached secular equilibrium with U-238, their parent isotope. Secular equilibrium means that the decay progeny of U-238 are being replaced at the same rate they are decaying; after 25 weeks all three isotopes are decaying at approximately the same rate. This is a maximum time; in reality, equilibrium will be reached much faster, since these two isotopes can never be separated totally from U-238. The isotope U-238 emits alpha particles and also emits some gamma rays. Its decay progeny Th-234 and Pa-234 each emit beta particles and gamma rays. An alpha particle is a fast helium atom with its two electrons removed, a beta particle is a high-speed electron and a gamma ray is like an X-ray.
From this analysis
we conclude that in a solid sample of DU, six months at most after manufacture of a DU penetrator, or DU armor for a tank, or DU particles in a person's body, substantial additional radiation in the form of beta particles and gamma rays always will be present. In fact, most of the penetrating gamma radiation and all of the penetrating beta radiation from DU comes, not from uranium, but from the decay progeny of U-238 (Ref. 15). In a year, only one-thousandth of a gram (1 milligram or mg) of DU generates more than a billion alpha particles, beta particles and gamma rays. The U.S. Army has investigated the generation of DU aerosols in armored vehicles hit by DU cannon rounds. Their investigators report "...that personnel inside DU struck vehicles could receive a dose in the `tens of milligrams' range due to inhalation" (Ref. 16). This exposure results in an acute dose of uranium.
http://www.wise-uranium.org/dgvd.htmlWhile uranium-238 is minimally radioactive, its decay products - Thorium 234 and Protactinium 234 - are beta particle emitters with half-lives about 20 days and one minute respectively (Pa 234 decays to Uranium 234, which has a half-life of hundreds of millennia, and this isotope does not build to equilibrium concentration for a very long time). When the two first isotopes in the decay chain reach their (tiny) equilibrium concentrations, a sample of initially pure uranium-238 will emit three times the radiation due to uranium-238 itself, and most of this will be beta radiation. After all the beta radiation is almost over, the by-product of uranium-238 would be (Pb) lead.
http://en.wikipedia.org/wiki/U238Fiction: Alpha particles can't penetrate clothes and skin.
Fact: This statement ignores the most prevalent and dangerous pathway for uranium to get into the human body. Inhaled uranium can remain in the lungs and bones for years where it continues to emit alpha, beta and gamma radiation. Each alpha particle can traverse up to several hundred cells causing somatic and genetic alterations. Multiply this by billions of such particles and a huge amount of cellular damage becomes possible. The majority (50-70%) of the airborne DU particles sampled during the testing of 105 mm DU projectiles were in the respirable range and capable of reaching the non-ciliated bronchial tree. Studies also indicate that the half-time in the lungs is up to 5 years.
Soluble DU compounds have rapid access to the bloodstream with consequent toxic effects on the target organs and the bone where it is incorporated. Mass spectrometry results of deceased Canadian veteran, Captain Terry Riordon, confirmed that depleted uranium was present in his bone. From there it can compromise the immune system and affect the stem cells that travel throughout the body thereby affecting many other organs. Soldiers inside a tank or armoured vehicle can inhale tens of milligrams of DU after the shell goes through the tank. Compare this to the maximum allowable yearly dose in the U.S. for inhaled uranium is 1.2 milligrams per year.
http://www.umrc.net/facts_and_fictions.aspx
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