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

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

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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 Saruhashi’s groundbreaking research focused on acid rain, radioactivity spread through oceans, and CO2 levels in seawater. 1. Time, "Who Is Katsuko Saruhashi? 5 Things to Know About the Pioneering Geochemist," 22 Mar. 2018 If the plume encountered storm clouds, a large amount of drifting fallout could suddenly descend, creating a hot spot of radioactivity many miles from ground zero. Daily Intelligencer, "This Is What a Nuclear Bomb Looks Like," 12 June 2018 The Hawaii researchers were curious to see whether coral skeletons near Enewetak would show evidence of this radioactivity. Elizabeth Svoboda, Scientific American, "Cores from Coral Reefs Hold Secrets of the Seas’ Past and Future," 6 June 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

History and Etymology for radioactivity

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Last Updated

31 Aug 2018

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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 \

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 \
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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to reject or criticize sharply

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