radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty ˌrā-dē-ō-ak-ˈti-və-tē How to pronounce radioactivity (audio)
: 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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The licensee has to reduce the residual radioactivity to levels that permit release of the property and termination of the facility’s operating license. Prabhat Ranjan Mishra, Interesting Engineering, 3 Oct. 2025 Because phosphorus-30 was created after bombarding aluminum with alpha particles – rather than occurring in its natural state – Irene and Frederic induced the radioactivity. Andrea Richard, The Conversation, 2 Oct. 2025 In the case of radioactivity, Tesla EVs appear harmless. Charles Singh, USA Today, 24 Sep. 2025 Adding more radioactivity to the Alaskan ecosystem would likely result in higher rates of cancer. Shoshi Parks, Popular Science, 14 Aug. 2025 See All Example Sentences for radioactivity

Word History

Etymology

International Scientific Vocabulary

First Known Use

1899, in the meaning defined above

Time Traveler
The first known use of radioactivity was in 1899

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Cite this Entry

“Radioactivity.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radioactivity. Accessed 6 Oct. 2025.

Kids Definition

radioactivity

noun
ra·​dio·​ac·​tiv·​i·​ty -ˌak-ˈtiv-ət-ē How to pronounce radioactivity (audio)
: 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 How to pronounce radioactivity (audio)
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

More from Merriam-Webster on radioactivity

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