radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty ˌrā-dē-ō-ak-ˈti-və-tē 

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

also : the rays emitted

Examples of radioactivity in a Sentence

Recent Examples on the Web

Inside, bright-yellow caution signs warned of radioactivity; photographs of lunar missions hung on the walls. —Dhruv Khullar, The New Yorker, 10 Feb. 2025

While a typical 28-gram serving of Brazil nuts contains 0.47 to 0.80 micro-sieverts, the maximum radioactivity found in a single mussel was 63.42 μSv. —Kevin Lynn, Newsweek, 7 Jan. 2025

Much of this waste arrives at facilities where workers attempt to treat and clean it, but often end up concentrating the radioactivity and becoming contaminated themselves. —Justin Nobel, Harper's Magazine, 2 Jan. 2025

Researchers need to design new materials that can decay within a few years to levels of radioactivity that can be disposed of safely and more easily. —Farhat Beg, The Conversation, 8 Jan. 2025

Word History

Etymology

International Scientific Vocabulary

First Known Use

1899, in the meaning defined above

Kids Definition

radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty -ˌak-ˈtiv-ət-ē 

: the giving off of rays of energy or particles by the breaking apart of atoms of certain elements (as uranium)

Medical Definition

radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty -ak-ˈtiv-ət-ē 

plural radioactivities

: 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