plutonium 239

plutonium

[ploo-toh-nee-uhm]
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.

Origin:
1940–45; < Greek Ploútōn Pluto + -ium

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World English Dictionary
plutonium (pluːˈtəʊnɪəm)
 
n
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
 
[C20: named after the dwarf planet Pluto because Pluto lies beyond Neptune and plutonium was discovered soon after neptunium]

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Etymonline
Word Origin & History

plutonium
1942, from Pluto, the planet (see Pluto), 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.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

plutonium plu·to·ni·um (plōō-tō'nē-əm)
n.
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.

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American Heritage
Science Dictionary
plutonium   (pl-tō'nē-əm)  Pronunciation Key 
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.
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American Heritage
Cultural Dictionary
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
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Published by Houghton Mifflin Company. All rights reserved.
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