Dictionary
ra•di•o•ac•tiv•i•ty
Pronunciation: (rā"dē-ō-ak-tiv'i-tē), [key]—
n. Physics, Chem.
the phenomenon, exhibited by and being a property of certain elements, of spontaneously emitting radiation resulting from changes in the nuclei of atoms of the element. Also called
activity. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.