Dictionary![]() ![]() plu•to•ni•umPronunciation: (plOO-tō'nē-um), [key] —n. Chem., 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; at. no.: 94. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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