Natural uranium in soil is about 1 to 3 parts per million, whereas in uranium ore it is about 1,000 times more concentrated, reaching about 0.05 to 0.2 percent of the total weight. Depleted uranium concentrate is almost 100 percent uranium. More than 99 percent of both natural and depleted uranium consists of the isotope U-238. One gram of pure U-238 has a specific activity of 12.4 kBq, which means there are 12,400 atomic transformations every second, each of which releases an energetic alpha particle. Uranium 238 has a half life of 4.51 E+9 (or 4.51 times 10 to the 9thpower, equivalent to 4,510,000,000 years).
Each atomic transformation produces another radioactive chemical: first, uranium 238 produces thorium 234, (which has a half life of 24.1 days), then the thorium 234 decays to protactinium 234 (which has a half life of 6.75 hours), and then protactinium decays to uranium 234 (which has a half life of 2.47E+5 or 247,000 years). The first two decay radioisotopes together with the U 238 count for almost all of the radioactivity in the depleted uranium. Even after an industrial process which separates out the uranium 238 has taken place, it will continue to produce these other radionuclides. Within 3 to 6 months they will all be present in equilibrium balance. Therefore one must consider the array of radionuclides, not just uranium 238, when trying to understand what happened when veterans inhaled depleted uranium in the Gulf War.
It should be noted that uranium 235, the more fissionable fraction which was partially removed in enrichment, makes up only 0.2 to 0.3 percent of the depleted uranium, whereas it was 0.7 percent of natural uranium. It is this deficit which enables one to use analytical methods to identify the uranium found in veteran's urine as depleted and not natural uranium. The U 235 was extracted for use in nuclear weapons and nuclear reactor fuel. Depleted uranium is considered nuclear waste, a by-product of uranium enrichment.
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