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 But the patterns of radioactivity the researchers observed in local honey added another layer to this story. Alex Fox, Smithsonian Magazine, "Fallout From Cold War Nuclear Testing Detected in U.S. Honey," 24 Apr. 2021 The tour, operated by Ukrainian International Airlines, will take place on April 25, the eve of the date that Chernobyl's Reactor No, 4 exploded in 1986, sending a toxic plume of radioactivity into the skies over Europe. Pavlo Fedykovych, CNN, "Dark tourism takes to the sky above Chernobyl," 21 Apr. 2021 The highest levels of radioactivity occurred in a Florida sample—19.1 becquerels per kilogram. Nikk Ogasa, Science | AAAS, "Nuclear fallout is showing up in U.S. honey, decades after bomb tests," 20 Apr. 2021 These fears were addressed instead by films that tickled the imagination, with giant insects transformed by radioactivity. Time, "Climate Change Is the Biggest Story on Earth. So Why Can’t Hollywood Make Good TV Shows and Movies About It?," 17 Apr. 2021 Unfortunately, the idea of releasing radioactivity of any sort makes most people cringe. James Conca, Forbes, "Japan Will Release Radioactive Fukushima Water Into The Ocean," 12 Apr. 2021 That’s because the seawater would buffer the pH. There is some radioactivity, but only slightly above regulatory standards, according to state Department of Environmental Protection, and probably not much of a health hazard. Larry Brand, The Conversation, "Water being pumped into Tampa Bay could cause a massive algae bloom, putting fragile manatee and fish habitats at risk," 8 Apr. 2021 Three reactor cores exploded, releasing the highest amount of radioactivity in the environment since the Chernobyl nuclear disaster. Meagan Cantwell, Science | AAAS, "Ten years later, here’s what Fukushima’s damaged reactors look like today," 19 Mar. 2021 Curie would publish a new paper on radioactivity in 1910, which led to her second Nobel Prize, this time a solo award in Chemistry. Peter Aitken, Fox News, "Marie Curie: What to know about the first woman to win Nobel Prize," 16 Mar. 2021

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.

See More

First Known Use of radioactivity

1899, in the meaning defined above

History and Etymology for radioactivity

International Scientific Vocabulary

Keep scrolling for more

Learn More about radioactivity

Time Traveler for radioactivity

Time Traveler

The first known use of radioactivity was in 1899

See more words from the same year

Statistics for radioactivity

Last Updated

27 Apr 2021

Cite this Entry

“Radioactivity.” Dictionary, Merriam-Webster, Accessed 7 May. 2021.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

Keep scrolling for more

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

More from Merriam-Webster on radioactivity

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

Comments on radioactivity

What made you want to look up radioactivity? Please tell us where you read or heard it (including the quote, if possible).


Test Your Vocabulary

Star Wars Words Quiz

  • cu jedi training
  • The bounty portion of bounty hunters (such as Boba Fett) comes from a Latin word meaning
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!