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protactinium

[ proh-tak-tin-ee-uhm ]

noun

, Chemistry.
  1. a radioactive, metallic element. : Pa; : 91.


protactinium

/ ˌprəʊtækˈtɪnɪəm /

noun

  1. a toxic radioactive metallic element that occurs in uranium ores and is produced by neutron irradiation of thorium. Symbol: Pa; atomic no: 91; half-life of the most stable isotope, 231Pa: 32 500 years; valency: 4 or 5; relative density: 15.37 (calc.); melting pt: 1572°C Former nameprotoactinium
“Collins English Dictionary — Complete & Unabridged” 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012


protactinium

/ prō′tăk-tĭnē-əm /

  1. A rare, extremely toxic, radioactive metallic element of the actinide series that occurs in uranium ores. It has 13 known isotopes, the most stable of which is protactinium 231 with a half-life of 32,760 years. Atomic number 91; approximate melting point 1,550°C; specific gravity 15.37; valence 4, 5.


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Word History and Origins

Origin of protactinium1

First recorded in 1915–20; prot- + actinium

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prot-protagonist