Plutonium

Plutonium, symbol Pu, radioactive metallic element that is used in nuclear reactors and nuclear weapons. The atomic number of plutonium is 94. The element is one of the transuranium elements in the actinide series of the periodic table (see Periodic Law).

Isotopes of plutonium were first prepared by the American chemist Glenn T. Seaborg and his associates at the University of California at Berkeley in 1940. Trace amounts of the element have since been found in uranium ores, but plutonium is prepared in relatively large quantities today in nuclear reactors. Plutonium was named for the planet Pluto.

Chemically, plutonium is reactive, its properties somewhat resembling those of the rare earth elements. The silvery metal, which becomes slightly yellow through oxidation caused by exposure to air, exists in six varying crystalline forms and has four different oxidation states. The metal gives off heat because of its radioactivity; 19 different isotopes of plutonium are known. Plutonium melts at about 641°C (about 1186°F) and boils at about 3228°C (about 5842°F). Each of plutonium’s six forms has a different specific gravity; they vary from to 16 to 19.9.

The most important isotope, plutonium-239, has a half-life of 24,100 years, and is produced by bombarding uranium-238 with slow neutrons. This forms neptunium-239, which in turn emits a beta particle and forms plutonium-239. Plutonium is the most economically important of the transuranium elements because plutonium-239 readily undergoes fission and can be both used and produced in quantity in nuclear reactors (see Nuclear Energy). It is also used in making nuclear weapons. It is an extremely hazardous poison due to its high radioactivity (see Radiation Effects, Biological). Plutonium-238 has been used to power equipment on the Moon by means of the heat it emits.