Posted: 10/06/2006 - 21:48
Natural Decay Chains
Uranium-radium chain -- Uranium-actinium chain -- Thorium chain
The nuclides generated during the decay of the very long-lived natural radionuclides U-238 (half-life 4.5 bn years), U-235 (half-life 0.7 bn years) and Th-232 (half-life 14 bn years) are in turn radioactive, and therefore decay again. Thus, the so-called decay chains are created which end only when a non-radioactive nuclide is formed. The uranium-radium decay chain starts from U-238 and ends via 18 intermediate states at the stable lead-206. Uranium-235 is at the beginning of the uranium-actinium decay chain leading via 15 radionuclides to lead-207. With ten intermediate states, the thorium decay chain starting with thorium-232 and ending at lead-208 is the shortest.
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