Main Entry: ra·dio·ac·tiv·i·ty

Pronunciation: \-ak-ˈti-və-tē\

Function: noun

Etymology: International Scientific Vocabulary

Date: 1899

: the property possessed by some elements (as uranium) or isotopes (as carbon 14) of spontaneously emitting energetic particles (as electrons or alpha particles) by the disintegration of their atomic nuclei; also : the rays emitted