ra·​dio·​ac·​tiv·​i·​ty | \ ˌrā-dē-ō-ak-ˈti-və-tē How to pronounce radioactivity (audio) \

Definition of radioactivity

: 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 incident correlates with an equally mysterious rise in radioactivity in sheep in nearby Australia, confirming that a nuclear test took place. Kyle Mizokami, Popular Mechanics, "Sheep Glands Point to Nukes as Source of Mysterious 1979 Explosion," 12 Sep. 2018 Marie Curie shared the prize in 1903 with Henri Becquerel and her husband Pierre Curie for their work on radioactivity. Jennifer Ouellette, Ars Technica, "2018 physics Nobel Prize honors 3, including first woman in 55 years," 2 Oct. 2018 To be clear, the theft of this particular radiological material isn’t that worrying by itself; the disks are sealed and contain less radioactivity than a smoke detector, according to a DOE official. Rachel Becker, The Verge, "The US government has trouble keeping track of radioactive material," 17 July 2018 The massive uranium deposit in Pittsylvania County, at the midpoint of the state’s border with North Carolina, was discovered decades ago, but in the 1980s the General Assembly prohibited mining because of concerns about radioactivity. Washington Post, "U.S. high court to take up issue of whether Virginia can ban a uranium mine," 21 May 2018 Kaltofen, through the course of his study, found three of the highest levels of thorium radioactivity in the dust of three Hanford workers’ homes. Hal Bernton, The Seattle Times, "Study: Traces of radioactive contamination found in homes of six Hanford workers," 14 June 2018 Tetra Tech worked on only one building on Parcel A, Building 322, which was scanned for radioactivity and then removed from the site in 2004. J.k. Dineen, San Francisco Chronicle, "Officials endorse safety at San Francisco Shipyard development site," 30 May 2018 Enrico Fermi was an architect of the atomic bomb, a father of radioactivity research, and a Nobel Prize–winning scientist who contributed to breakthroughs in quantum mechanics and theoretical physics. Derek Thompson, The Atlantic, "But, Seriously, Where Is Everybody?," 22 June 2018 Some flashes occur as a result of collisions by stray neutrons and other background radioactivity. Davide Castelvecchi, Scientific American, "Beguiling Dark-Matter Signal Persists 20 Years on," 2 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'radioactivity.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of radioactivity

1899, in the meaning defined above

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The first known use of radioactivity was in 1899

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More Definitions for radioactivity


ra·​dio·​ac·​tiv·​i·​ty | \ ˌrā-dē-ō-ak-ˈti-və-tē How to pronounce radioactivity (audio) \

Kids Definition of radioactivity

1 : the giving off of rays of energy or particles by the breaking apart of atoms of certain elements (as uranium)
2 : the rays or particles that are given off when atoms break apart


ra·​dio·​ac·​tiv·​i·​ty | \ -ak-ˈtiv-ət-ē How to pronounce radioactivity (audio) \
plural radioactivities

Medical Definition of radioactivity

: 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

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Spanish Central: Translation of radioactivity

Nglish: Translation of radioactivity for Spanish Speakers Encyclopedia article about radioactivity

Comments on radioactivity

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a strong desire or propensity

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