Dictionaryac•ti•nonPronunciation: (ak'tu-non"), [key] —n. Chem. a chemically inert, gaseous, short-lived isotope of radon that is a member of the actinium series. Symbol: An; at. no.: 86; at. wt.: 219. Also called actinium emanation. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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