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

The licensee has to reduce the residual radioactivity to levels that permit release of the property and termination of the facility’s operating license. —Prabhat Ranjan Mishra, Interesting Engineering, 3 Oct. 2025

Because phosphorus-30 was created after bombarding aluminum with alpha particles – rather than occurring in its natural state – Irene and Frederic induced the radioactivity. —Andrea Richard, The Conversation, 2 Oct. 2025

In the case of radioactivity, Tesla EVs appear harmless. —Charles Singh, USA Today, 24 Sep. 2025

The level of cesium 137 detected in the frozen shrimp was about 68 becquerels per kilogram, a measure of radioactivity. —Emma Burleigh, Fortune, 23 Sep. 2025

Word History

Etymology

International Scientific Vocabulary

First Known Use

1899, in the meaning defined above

Rhymes for radioactivity

• bioactivity
• commutativity
• cooperativity
• generativity
• hyperactivity
• insensitivity
• interactivity
• overactivity
• performativity
• retroactivity
• absorptivity
• affectivity

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