Write about Uranium atom.

     

Uranium is a chemical element with the symbol U and atomic number 92.  It is a silvery-grey metal in the actinide series of the periodic table.  A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons.  Uranium is weakly radioactive because all isotope of uranium are unstable; the half-lives of its naturally occurring isotope range between 159,200 years and 4.5 billion years.  The most common isotope in natural uranium are uranicum-238 and uranium-235.  

     Uranium has the highest atomic weight of the primordially occurring elements.  Its density is about 70% higher than that of lead, and slightly lower than that of gold or tungsten.  It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.  

     Many contemporary uses of uranium exploit its unique nuclear properties.  Uranium-235 is the only natrually occurring fissile isotope, which makes it widely used in nuclear power plants and nuclear weapons.  However, because of the tiny amounts found in nature, uranium needs to undergo enrichement so that enough uranium-235 is present.  Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissible plutonium-239  in a nuclear reactor.  Another fissile isotope, uranium-233, can be produced from natrual thorium and is studied for future industrial use in nuclear technology.  Uranium-238 has a mall probability for spontaneous fission or even induced fission with fast neutrons;  Uranium-235 and to a lesser degree uranoum-233 have a much higher fission cross-section for slow neutrons.