Plutonium
Plutonium is a highly reactive, silvery-white metal element denoted by the atomic symbol, Pu. Its atomic number is 94 and it has an atomic weight of approximately 244. It is a transuranium element in the actinide series. Fifteen isotopes of plutonium are known.
Plutonium is a man-made element first created during the mid-twentieth century. After his discovery of neptunium in 1940, Edwin McMillan felt sure that a second transuranium element was present among the products of the nuclear fission of uranium that he had been studying. When he left Berkeley, California, in November 1940, McMillan suggested to Glenn Seaborg that he look for that element. Only a month later, with colleagues A. C. Wahl and J. W. Kennedy, Seaborg isolated the element. They chose to name their discovery plutonium (chemical symbol: Pu) after the planet Pluto. The decision followed the pattern of naming uranium after Uranus and neptunium after Neptune. News of plutonium's discovery was sent to professional journals in early 1941. But because of wartime secrecy regulations, these reports were not published until 1946.
Plutonium has a melting point of 1,184°F (640°C). Its estimated abundance in the earth's crust is 10-22 percent. Like neptunium, plutonium is formed in very small amounts as the result of the radiation of uranium by naturally occurring neutron s.
Plutonium is a highly reactive element. At room temperature, it is warm to the touch. Large pieces release enough energy to cause water to boil. The pure metal can be produced by heating plutonium (III) fluoride with calcium or barium vapors at 2,192°F (1,200°C).
Plutonium is by far the most important of the transuranium elements. Other than uranium-235 and uranium-233, plutonium is the only fissionable isotope known. As such, it is critically important in the manufacture of nuclear weapons and nuclear power plants. The fission of a single kilogram of the element releases 22 million kilowatt hours of heat energy.
Plutonium is considered one of the most toxic materials known. Concentrations of more than 6 x 10-13 microcuries per cubic centimeter of air are considered very dangerous.
By some estimates, 20,000 kilograms of the element are produced each year as a by-product in nuclear power reactors. Upwards of 500,000 kilograms of the element may now be available from such sources. In addition to its applications in power reactors and nuclear weapons, plutonium is used in thermoelectric generators, where the heat energy it releases is converted into electricity. Artificial heart pacemakers may contain a very small quantity of plutonium as a source of electricity.
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