|Atomic mass||238.029 amu|
Uranium was discovered in 1789 in a sample of mineral pitchblende. The property of radioactivity was not discovered until 1896. It is named after the planet, Uranus.
Uranium is widely distributed in the earth's crust. Its most important ore being uraninite, an oxide of variable composition approximating UO2. Pitchblende is one form of uraninite, of composition U3O8. There are several uranium-producing mines in Canada located in Elliot Lake, Espanola and Bancroft regions of Ontario and Beaverlodge in Northern Saskatchewan. Other important deposits occur in Australia, U.S.A. and Africa.
The concentration of uranium found in the ore is only 0.1 to 0.2%. This is concentrated to 60 to 70% at the mine by a leaching process followed by ion exchange or solvent extraction. It is refined in the Port Hope, Ontario facility of Eldorado Nuclear Ltd. into fuels for nuclear reactors or uranium metal for radiation shielding and other applications.
Uranium has become an extremely important element, mainly because of its potential to provide nuclear energy. The principal isotope, uranium-238, comprises 99.28% of the metal but is not subject to fission. Uranium-235, present to only 0.7%, is the only isotope of uranium that can be split by neutron bombardment to yield nuclear energy. Separation of the very small amount of uranium-235 from the nonfissionable uranium-238 was one of the biggest achievements of the Manhattan Project (1941) which developed the original "atomic" bomb. The energy yield per atom of 235 is about 200 million electron volt, plus two to three neutrons, which in turn initiate new fissions.