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

Physicists rely on them (opens a new tab) to unify the fundamental forces of nature: At high energies, group theory can be used to show that electromagnetism and the forces that hold atomic nuclei together and cause radioactivity are all manifestations of a single underlying force. —Leila Sloman, Quanta Magazine, 6 Sep. 2024

About 40 percent of the radioactivity comes from the element cesium-137, which has a half-life of 30 years, meaning its radioactivity is reduced by half every 30 years. —Philip Diehl, The Mercury News, 12 Aug. 2024

Today, the lab, preserved with some of its original equipment and archives, and its adjacent galleries tell the story of the Curie family’s impact on science, the radium craze that followed its 1898 discovery and the history of radioactivity in cancer treatment. —Shoshi Parks, Smithsonian Magazine, 5 July 2024

Due to corporate malfeasance, pollution has overwhelmed the city, leading to disturbing cases of radioactivity. —Barry Levitt, Vulture, 26 Feb. 2024

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