protactinium

American  

[proh-tak-tin-ee-uhm] / ˌproʊ tækˈtɪn i əm /

noun

Chemistry.

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

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protactinium British  

/ ˌprəʊtækˈtɪnɪəm /

noun

1. Former name: protoactinium.  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, ²³¹ Pa: 32 500 years; valency: 4 or 5; relative density: 15.37 (calc.); melting pt: 1572°C

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protactinium Scientific  

/ prō′tăk-tĭn′ē-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.

2. See Periodic Table

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Etymology

Origin of protactinium

First recorded in 1915–20; prot- + actinium