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[ploo-toh-nee-uh m] /pluˈtoʊ ni əm/
noun, Chemistry, Physics.
a transuranic element with a fissile isotope of mass number 239 (plutonium 239) that can be produced from non-fissile uranium 238, as in a breeder reactor. Symbol: Pu; atomic number: 94.
1940-45; < Greek Ploútōn Pluto + -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for plutonium
  • The other bomb would use plutonium-an element that had not been.
  • Spent fuel is rich in plutonium and leftover uranium-valuable nuclear material that the plant is designed to salvage.
  • The low- and medium-level radioactive material includes toxic uranium, rhodium, and plutonium.
  • Also, the second reactor uses plutonium fuel, which makes the situation worse.
  • There is no bomb grade uranium produced nor plutonium.
  • Some are getting rid of their stocks of highly enriched uranium or plutonium, both used in bombs.
  • He was to stop making plutonium as well as suspected work on uranium.
  • It run on natural uranium and was capable of producing weapons-grade plutonium.
  • Spent nuclear fuel contains plutonium, which can be extracted and used in new fuel.
  • The atomic electricity generation industry was created to make plutonium production less expensive for the military lobby.
British Dictionary definitions for plutonium


a highly toxic metallic transuranic element. It occurs in trace amounts in uranium ores and is produced in a nuclear reactor by neutron bombardment of uranium-238. The most stable and important isotope, plutonium-239, readily undergoes fission and is used as a reactor fuel in nuclear power stations and in nuclear weapons. Symbol: Pu; atomic no: 94; half-life of 239Pu: 24 360 years; valency: 3, 4, 5, or 6; relative density (alpha modification): 19.84; melting pt: 640°C; boiling pt: 3230°C
Word Origin
C20: named after the dwarf planet Pluto because Pluto lies beyond Neptune and plutonium was discovered soon after neptunium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for plutonium

transuranic element, 1942, from Pluto, the planet, + element ending -ium. Discovered at University of California, Berkeley, in 1941, the element named on suggestion of Seaborg and Wahl because it follows neptunium in the periodic table as Pluto follows Neptune in the Solar System. The name plutonium earlier had been proposed for barium and was sometimes used in this sense early 19c.

Online Etymology Dictionary, © 2010 Douglas Harper
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plutonium in Medicine

plutonium plu·to·ni·um (plōō-tō'nē-əm)
Symbol Pu
A naturally radioactive, metallic transuranic element, occurring in uranium ores or produced artificially by neutron bombardment of uranium. Its longest-lived isotope is Pu 244 with a half-life of 77 million years. Atomic number 94; melting point 640°C; boiling point 3,228°C; specific gravity 19.84; valence 3, 4, 5, 6.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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plutonium in Science
Symbol Pu
A silvery, radioactive metallic element of the actinide series that has the highest atomic number of all naturally occurring elements. It is found in minute amounts in uranium ores and is produced artificially by bombarding uranium with neutrons. It is absorbed by bone marrow and is highly poisonous. Plutonium is used in nuclear weapons and as a fuel in nuclear reactors. Its longest-lived isotope is Pu 244 with a half-life of 76 million years. Atomic number 94; melting point 640°C; boiling point 3,232°C; specific gravity 19.84; valence 3, 4, 5, 6. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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plutonium in Culture
plutonium [(plooh-toh-nee-uhm)]

A radioactive chemical element that is artificially derived from uranium.

Note: Plutonium is used in nuclear reactors.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Encyclopedia Article for plutonium


radioactive chemical element of the actinoid series of the periodic table, atomic number 94. It is the most important transuranium element because of its use as fuel in certain types of nuclear reactors and as an ingredient in nuclear weapons. Plutonium, warm because of energy released in alpha decay, is a silvery metal that takes on a yellow tarnish in air. The element was first detected (1941) as the isotope plutonium-238 by Glenn T. Seaborg, Joseph W. Kennedy, and Arthur C. Wahl, who produced it by deuteron bombardment of uranium-238 in the 60-inch cyclotron at Berkeley, California. Traces of plutonium have subsequently been found in uranium ores, where it is not primeval but naturally produced by neutron irradiation

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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