protactinium(redirected from Element 91)
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n. Symbol Pa
A rare, extremely toxic, radioactive, lustrous, metallic element having more than 30 known isotopes and isomers, the most common of which is Pa-231 with a half-life of 32,760 years. Atomic number 91; atomic weight 231.036; melting point 1,572°C; specific gravity 15.37 (calculated); valence 2, 3, 4, 5. See Periodic Table.
(Elements & Compounds) 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 name: protoactinium
prot•ac•tin•i•um(ˌproʊ tækˈtɪn i əm)
a radioactive, metallic chemical element. Symbol: Pa; at. no.: 91.
Symbol Pa A rare, extremely toxic, radioactive metallic element of the actinide series that occurs in uranium ores. Its most common isotope has a half-life of 32,500 years. Atomic number 91. See Periodic Table.
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|Noun||1.||protactinium - a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead|