Mesothorium Mes`o*tho"ri*um, n. [NL.; meso- + thorium.] (Chem.) a radioactive isotope of radium (radium-228) with a half-life of 5.8 years. Also called {mesothorium-1} or {mesothorium I} to distinguish it from a subsequent decay product, mesothorium II (actinium-228). It was discovered in 1907 by Otto Hahn as a decay product of thorium (produced by decay of thorium-232). Mesothorium-1 (radium-228) in turn produces actinium-228 (mesothorium-2) as the first product of its radioactive decay, and the actinium-228 in turn decays quickly (half-life of 6 hours) to thorium-228 (which is also called {radiothorium}; the thorium-228 has a half-life of 1.91 years, shorter than that of the radium-228). It was discovered and named before full recognition of the nature of isotopes of the elements, and was distinguished from other variants of radium by its half-life and mode of production and decay. It was also cheaper to prepare than other short-lived radium isotopes, and was thus sold commercially, for use, e.g. in making watch dials readable in the dark by painting the hands and hour marks with a self-luminous paint containing the radioactive substance; it is therefore often referred to (e.g. in regulatory legislation) as though distinct from radium. It was one of the isotopes believed responsible for radiation-induced diseases observed in industrial workers who painted radium on watch dials in the late 1950's and early 1960's. The primary isotope of radium (radium-226) has a half-life of 1620 years, and these isotopes with shorter half-lives proved difficult to isolate and study for the purpose of finding the cause of such diseases. [Webster 1913 Suppl. +PJC]

The Collaborative International Dictionary of English. 2000.

Look at other dictionaries:

  • mesothorium — [mes΄ōthôr′ē əm, mez΄ōthôr′ē əm] n. 〚ModL: see MESO & THORIUM〛 1. a radioactive isotope of radium (mesothorium 1), formed from thorium 2. a radioactive isotope of actinium (mesothorium 2) …   Universalium

  • mésothorium — ● mésothorium nom masculin Nom de deux noyaux radioactifs : le radium 228 (mésothorium 1) et l actinium 228 (mésothorium 2). [Ces produits sont utilisés en cancérologie pour la pénétration de leur rayonnement.] mésothorium [mezotɔʀjɔm] n. m. ÉTYM …   Encyclopédie Universelle

  • Mesothorium — oder Mesothor ist eine historische Bezeichnung für zwei radioaktive Nuklide: Mesothorium I, 228Ra, siehe Radium Mesothorium II, 228Ac, siehe Actinium Siehe auch: Zerfallsreihe#Historische Bezeichnungen …   Deutsch Wikipedia

  • mesothorium — [mes΄ōthôr′ē əm, mez΄ōthôr′ē əm] n. [ModL: see MESO & THORIUM] 1. a radioactive isotope of radium (mesothorium 1), formed from thorium 2. a radioactive isotope of actinium (mesothorium 2), formed from this isotope of radium …   English World dictionary

  • Mesothorium — Mesothorium, s. Thorium …   Lexikon der gesamten Technik

  • Mesothorium — Me|so|tho|ri|um 〈n.; s; unz.; Chem.〉 radioaktives Zerfallsprodukt des Thoriums ● Mesothorium I Isotop des Radiums; Mesothorium II Isotop des Aktiniums [<grch. mesos „mittel , mitten“ + Thorium] * * * Me|so|tho|ri|um [↑ meso (1)], das; s;… …   Universal-Lexikon

  • Mesothorium — Me|so|tho|ri|um 〈n.; Gen.: s; Pl.: unz.; Abk.: MsTh; Chemie〉 verschiedene radioaktive Zerfallsprodukte des Thoriums, z. B. ist Mesothorium I ein Radiumisotop, Mesothorium II ein Actiniumisotop [Etym.: <Meso… + Thorium] …   Lexikalische Deutsches Wörterbuch

  • mesothorium — |me]zō, |mē], ]sō+ noun Etymology: New Latin, from mes + thorium : either of two radioactive products intermediate between thorium and radiothorium in the thorium series or a mixture of the two products obtained usually from thorium minerals (as… …   Useful english dictionary

  • mesothorium — noun Any product of the radioactive decay of thorium, mainly isotopes of radium and actinium …   Wiktionary

  • mesothorium — The first two disintegration products of thorium; m. 1 is 228Ra, a beta emitter with a half life of 6.7 years, decaying into m. 2, which is 228Ac, a beta emitter with a half life of 6.13 hr, which disintegrates to radiothorium (228Th) …   Medical dictionary

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