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The discovery of uranium is commonly credited to Martin H. Klaproth, who in 1789, while experimenting with pitchblende, concluded that it contained a new element, which he named after the planet Uranus, discovered only eight years earlier. However, the substance that Klaproth identified was not pure uranium but an oxide. Eugene M. PEligot isolated the element in 1841. Antoine H. Becquerel discovered its radioactivity in 1896. Before the discovery of nuclear fission by Otto Hahn and Fritz Strassmann in 1939, the principal use of uranium (chiefly as the oxides) was in pigments, ceramic glazes, and a yellow-green fluorescent glass and as a source of radium for medical purposes. It has also been added to steels to increase their strength and toughness. However, because of the high toxicity (both chemical and radiological) of uranium and its compounds, and because of their importance as nuclear fuel, these earlier uses have been largely curtailed.
Uranium gained importance with the development of practical uses of nuclear energy. Uranium-235 is the only naturally occurring nuclear fission fuel, but this isotope is only about 1 part in 140 of natural uranium; the balance is mostly uranium-238. Because the supply of uranium-235 is limited, the use of fast breeder reactors that convert nonfissionable uranium-238 to fissionable plutonium-239 is becoming increasingly important (see nuclear reactor). Uranium-235 can be separated from uranium-238 by a diffusion process using the gaseous hexafluoride, UF6 ; the compound of the lighter isotope diffuses faster.
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