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

In the years following her Paris sojourn, Rona started to explore the phenomenon of radioactivity in seawater. New York Times, "Overlooked No More: Elizabeth Rona, Pioneering Scientist Amid Dangers of War," 28 Aug. 2019 Analyzing a Warren stump speech without making reference to substance is akin to writing a biography of Marie Curie without mentioning radioactivity. Walter Shapiro, The New Republic, "Arguing the World," 15 Aug. 2019 After the Chernobyl Nuclear Power Plant exploded in 1986, spewing radioactivity into the atmosphere, a 1,000-square-mile Exclusion Zone was established around the area hardest hit by the disaster. Brigit Katz, Smithsonian, "Why Scientists Are Making Vodka in the Chernobyl Exclusion Zone," 8 Aug. 2019 The Pentagon wants a reactor capable of making 1 to 10 megawatts of electricity, and is clear that the reactor needs to be safe, incapable of melting down and contaminating nearby troops with harmful radioactivity. Kyle Mizokami, Popular Mechanics, "Critics Roast the Department of Defense’s Battlefield Nuclear Reactor," 25 Feb. 2019 An explosion at a Russian military base killed three personnel and caused a brief spike in radioactivity in a nearby Russian city. Kyle Mizokami, Popular Mechanics, "Missile Explosion Prompts Radiation Warnings in Russia," 8 Aug. 2019 The imminent blockbuster and Finals MVP’s free agency looms over the entire NBA, yet here were Ball and James, in the flesh, laughing and dapping and … oh wait, there’s another spike in radioactivity on the other end of the floor. Jake Fischer,, "Zion Williamson Creates Raucous Atmosphere in Summer League Debut," 5 July 2019 Unprotected persons caught in the blast—or venturing into the blast zone afterward—could be exposed to dangerous levels of radioactivity, leading to radiation sickness or cancer. Kyle Mizokami, Popular Mechanics, "The Pentagon Wants VR To Train for Nuclear War," 9 July 2019 The first piece of land transferred to the city, a 75-acre hilltop region known as Parcel A, was not tested for radioactivity. Jason Fagone,, "Report: Navy altered Hunters Point cleanup to cover, not remove, toxic soil," 14 Aug. 2019

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

12 Oct 2019

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Time Traveler for radioactivity

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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More from Merriam-Webster on radioactivity

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Spanish Central: Translation of radioactivity

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

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