tho·​ri·​um | \ˈthȯr-ē-əm \

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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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 Inhalation of the particles, which included uranium, thorium, plutonium and americium, can increase the risk of cancer. Hal Bernton, The Seattle Times, "Study: Traces of radioactive contamination found in homes of six Hanford workers," 14 June 2018 Radiation occurs naturally in sand through elements like thorium, and techniques like radiocarbon dating use similar principles. David Grossman, Popular Mechanics, "New Study Shows Full Extent of Radiation Damage to Hiroshima Victims," 1 May 2018 Uranium-thorium dating of rock deposited over paintings in all three caves indicates that the paintings can’t be any younger than 64,000 years. Kiona N. Smith, Ars Technica, "Neanderthals were artists and thought symbolically, new studies argue," 22 Feb. 2018 But not all researchers agree that uranium-thorium dates are valid. Lorraine Boissoneault, Smithsonian, "Were Neanderthals the Earliest Cave Artists? New Research in Spain Points to the Possibility," 22 Feb. 2018 By comparing the ratios of uranium and thorium present in the bone, scientists can tell its age. Michael Price, Science | AAAS, "Human finger bone points to an early exodus out of Africa," 9 Apr. 2018 Uranium-thorium dating of carbonate minerals is often a better option. Chris Standish, Newsweek, "What Makes Us Human? Discovery of Neanderthal Art Is Rewriting What We Know About Ourselves," 27 Feb. 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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1 Oct 2018

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The first known use of thorium was in 1832

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tho·​ri·​um | \ˈthōr-ē-əm, ˈthȯr- \

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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