from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A radioactive silvery-white metallic element that is recovered commercially from monazite. Its longest-lived isotope, the only one that occurs naturally, is Th 232 with a half-life of 1.41 × 1010 years. It is used in magnesium alloys, and isotope 232 is a source of nuclear energy. Atomic number 90; atomic weight 232.038; approximate melting point 1,750°C; approximate boiling point 4,500°C; approximate specific gravity 11.7; valence 4. See Table at element.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. a chemical element (symbol Th) with atomic number 90.

from the GNU version of the Collaborative International Dictionary of English

  • n. A metallic element found in certain rare minerals, as thorite, pyrochlore, monazite, etc., and isolated as an infusible gray metallic powder which burns in the air and forms thoria; -- formerly called also thorinum. Symbol Th. Atomic weight 232.0.

from The Century Dictionary and Cyclopedia

  • n. In 1900 Brauner announced his belief that, thorium, as generally known, is separable into two different elements. A little later Baskerville, working by a different method, came to the same conclusion, and in 1903 claimed to have effected its separation into three components, for two of which he proposed the new names carolinium and berzelium, retaining the name thorium for the third component. Later he found for this new or purified thorium an atomic weight of 220.1–220.6. In 1905 R. J. Meyer and A. Gumperz published the results of a careful revision of the previous work on this subject, which they found did not afford any evidence in support of the earlier claims of the separability of thorium. Thorium is a radioactive element and is the parent of a series of radioactive products of which eight separate members have already been identified. These are known as mesothorium 1, mesothorium 2, radiothorium, thorium X, thorium emanation, thorium A, thorium B, and thorium C, and are ordinarily present in thorium compounds. Thorium and its products appear to constitute a separate radioactive group or family, distinct from the uranium group, of which actinium, ionium, radium, and polonium are members, although generally found associated with it in minerals. Thorium itself emits only a-rays, but, owing to the presence of thorium disintegration-products, β- and γ-rays are also given out by thorium compounds.
  • n. Chemical symbol, Th; atomic weight, 231.9. The metallic base of the earth thoria, discovered by Berzelius, in 1828, in a mineral from Norway, to which the name of thorite is now given, and which consists essentially of the silicate of thorium.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands


from The American Heritage® Dictionary of the English Language, 4th Edition

After Thor.

from Wiktionary, Creative Commons Attribution/Share-Alike License

After Thor.


  • These are mostly mined for the rare earths; the thorium is a low-value waste product.

    Dennis Wingo - Why Space? Why Now? - NASA Watch

  • I've read the Los Alamos reports, but I'd like to know if, since then anyone has said the thorium is more concentrated than being a constituent of KREEP overturned at basin rim structures.

    Dennis Wingo - Why Space? Why Now? - NASA Watch

  • Nuclear fuel, ie uranium and potentially thorium, is incredibly abundant and currently inexpensive.

    Coyote Blog » Blog Archive » Should We Take Another Shot at Nuclear Power?

  • Let it suffice to call to mind how it proved possible to produce from certain thorium minerals lead with precisely the same chemical properties as ordinary lead, but with considerably higher atomic weight - that is to say, an isotope to lead.

    Nobel Prize in Chemistry 1921 - Presentation Speech

  • If the metal thorium is exposed in a reactor to neutron bombardment, it may be transformed into a fissionable isotope of uranium having a mass 233.

    The Peacetime Applications of Atomic Energy

  • The Atomic Energy Commission is concerned mainly with fundamental research work at the universities and in the Tata Institute of Fundamental Research in Bombay and with problems associated with the discovery of uranium and the processing of thorium from the huge monazite sand deposits of southern India.

    Atom and Empire

  • Nuclear power from fusion might one day be an especially promising field, as may be the use of the radioactive chemical element thorium, which is more abundant than uranium and awaits harnessing.

    Post-Carbon America

  • Recent discoveries at the lab include a cheaper method of producing the element thorium, which is viewed as a potential sustainable energy source; so-called NanoBeacons that are silver atoms that glow different colors when they attach to certain acids and can help in diagnosing disease; and a special drilling fluid to help prevent massive oil spills, such as the one that happened last year in The Gulf.

    Crews battle N.M. fire as it pushes into canyon

  • This isotope also does not occur in nature, but can be bred from the element, thorium, which is very common.

    Victor Stenger: LFTR: A Long-Term Energy Solution?

  • According to geologists, it is the only known commercial deposit of rare earths in the world that has virtually no contamination from thorium, which is radioactive.

    NYT > Home Page


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    December 1, 2007