uranium

Traductions

• anglais

  Date : 1983

  Définition

  An element. State: Solid; Group: IIIB (Actinide Series); Atomic No.: 92; Atomic Wt.: 238.209; Valence: 3,4,6; Isotopes: 3 natural radioactive. A heavy and strongly radioactive metal, m.p. 1132 °C (2070 °F), extracted from the ores pitchblende and carnotite occurring chiefly in the African Congo, Canada, and Colorado. The principal isotope, U-238, comprises 99% of the metal but is not subject to fission. The 235 isotope, present to only 0.7%, stands at the top of the actinide decay series. It is this isotope that can be split by neutron bombardment to yield nuclear energy. The artificial isotope U-233, derived from thorium, is also fissionable. The third natural isotope, U-234, has little importance.

  Note :

  Separation of the very small amount of U-235 from the nonfissionable U-238 was one of the chief achievements of the Manhattan Project (1941) which developed the original "atomic" bomb; separations were effected by gaseous diffusion (uranium hexafluoride, UF₆, through porous barrier sequences) and by electromagnetic means. The energy yield per atom of 235 is about 200 million electron volts, plus two to three neutrons, which in turn initiate new fissions. Plutonium is made from uranium by absorption of two neutrons.

  Termes :

  1. uranium
  2. U

  [U] Symbol for the element uranium, the name being adopted from the planet Uranus which was thought to be the outermost planet of the solar system at the time the element was discovered, 1789.