tho·​ri·​um | \ ˈthȯr-ē-əm How to pronounce thorium (audio) \

Definition of thorium

: a radioactive metallic element that is obtained especially from monazite and is usually associated with rare earths — see Chemical Elements Table

Examples of thorium in a Sentence

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Uranium-thorium dating of the calcite that had run over the art (a red dot, a red ladder, a red hand-stencil) showed this art to have been made, there in the darkness, around 65,000 years BP. Tobias Carroll, Longreads, "‘The Underland Is a Deeply Human Realm’: Getting Down with Robert Macfarlane," 20 June 2019 Ores containing these rare earths typically contain radioactive material like thorium. Klint Finley, WIRED, "Are Rare Earths the Next Pawn in the US-China Trade War?," 17 June 2019 As Laura Geggel reports for Live Science, the first of the dating techniques the researchers used measured uranium and thorium’s decay into helium to calculate the age of small zircon crystals retrieved from the site. Meilan Solly, Smithsonian, "Rock Art and Footprints Reveal How Ancient Humans Responded to Volcanic Eruption," 4 June 2019 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 But thorium couldn't produce anywhere near the energy the Orville would require. Jennifer Ouellette, Ars Technica, "The Orville blends science fiction and science fact into a winning mix," 29 Dec. 2018 The older a flowstone gets, the more thorium builds up inside it. Carl Zimmer, New York Times, "Neanderthals, the World’s First Misunderstood Artists," 22 Feb. 2018 Mass spectrometer analysis shows how much of the trace uranium in the core’s layers has decayed to thorium, and the ratio between the two elements is used to calculate each layer’s approximate age. Elizabeth Svoboda, Scientific American, "Cores from Coral Reefs Hold Secrets of the Seas’ Past and Future," 6 June 2018 In addition to beryllium, the soil contains lead and radioactive elements of thorium, radium and uranium. Keith Matheny, Detroit Free Press, "Radioactive soil from Ohio heads to Wayne County landfill next week," 22 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'thorium.' 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 thorium

1832, in the meaning defined above

History and Etymology for thorium

New Latin, from Old Norse Thōrr Thor

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25 Jun 2019

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The first known use of thorium was in 1832

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tho·​ri·​um | \ ˈthōr-ē-əm, ˈthȯr- How to pronounce thorium (audio) \

Medical Definition of thorium

: a radioactive metallic element that occurs combined in minerals and is usually associated with rare earths symbol Th — see Chemical Elements Table

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