The Fission Of Uranium
By far the most important characteristic of uranium is that it undergoes the nuclear reaction called fission. Uranium-235, which is only about 0.7% of all uranium atoms, is the isotope that fissions most readily. For use in nuclear reactors, natural uranium is enriched in the 235 isotope (that is, the percentage of the 235 isotope is increased) by gaseous diffusion. In this process the uranium is converted into the gaseous compound uranium hexafluoride, UF6, and allowed to diffuse through a series of porous barriers. Those molecules which contain atoms of the slightly lighter uranium-235 isotope diffuse slightly faster and therefore separate themselves from the heavier, more slowly moving molecules that contain uranium-238.
See also Element, chemical.
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Robert L. Wolke