uranium 238


: an isotope of uranium of mass number 238 that is the most stable uranium isotope, that constitutes over 99 percent of natural uranium, that is not fissile but can be used to produce a fissile isotope of plutonium, and that has a half-life of 4.5 billion years

Example Sentences

Recent Examples on the Web Most of the rest of our planet’s inner warmth now comes from the radionuclides thorium 232 and uranium 238. Marcus Woo, Scientific American, 17 Nov. 2020 The centrifuges are used to separate the rare, highly radioactive isotope, uranium 235, from the less radioactive type, uranium 238. BostonGlobe.com, 5 Nov. 2019 The centrifuges are used to separate the rare, highly radioactive isotope, uranium 235, from uranium 238. David E. Sanger, New York Times, 4 Nov. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'uranium 238.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History

First Known Use

1942, in the meaning defined above

Time Traveler
The first known use of uranium 238 was in 1942

Dictionary Entries Near uranium 238

Cite this Entry

“Uranium 238.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/uranium%20238. Accessed 2 Dec. 2022.

Kids Definition

uranium 238


: the most stable form of uranium that has an atomic mass number of 238, breaks down in a series of nuclear changes into a form of lead, and can absorb neutrons and then go through a series of nuclear transformations to change into a form of plutonium
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