/proh'tak tin"ee euhm/, n. Chem.
a radioactive, metallic element. Symbol: Pa; at. no.: 91.
[1915-20; PROT- + ACTINIUM]

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 radioactive chemical element of the actinoid series of the periodic table, rarer than radium; its atomic number is 91. It occurs in all uranium ores to the extent of 0.34 part per million of uranium and was first isolated (1934) in metallic form by Aristid V. Grosse. The first isotope, protactinium-234, was discovered (1913) by Kasimir Fajans and O.H. Göhring and named brevium, afterward uranium X2, because it was a short-lived member of the uranium radioactive decay series. The long-lived isotope protactinium-231 (originally called protoactinium) was discovered (1917) independently by Otto Hahn and Lise Meitner in pitchblende, by Fajans, and by Frederick Soddy, John Cranston, and Sir Alexander Fleck. This isotope decays to actinium-227 with a half-life of 32,500 years.

      All of the more than a dozen isotopes are radioactive; synthetic protactinium-233 is the progenitor of the fissile uranium isotope uranium-233 in the production of nuclear fuel from thorium. Protactinium in most of its compounds exhibits an oxidation state of +5 (thus resembling tantalum) but also can be obtained in the +4 state. Its compounds readily hydrolyze in water, forming colloids, but dissolve by forming complex ions (as with the fluoride ion in hydrofluoric acid).

atomic number
stablest isotope
oxidation states
+4, +5
electronic config.

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Universalium. 2010.

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  • PROTACTINIUM — Le protactinium (Pa) est l’élément chimique de numéro atomique 91. Tous ses isotopes sont radioactifs; deux d’entre eux existent dans la nature associés à la géochimie de l’uranium. L’isotope de masse 231, émetteur 見 de période 1/2 = 34 000 ans,… …   Encyclopédie Universelle

  • Protactinium — Thorium ← Protactinium → Uranium Pr …   Wikipédia en Français

  • Protactinium — The radioactive chemical element, of atomic number 91; Atomic symbol Pa; at. wt. of longest lived isotope, 231 (T1/2 = 32,500 yrs.) Also called brevium, Uranium X2 and UX2. [PJC] …   The Collaborative International Dictionary of English

  • protactinium — Symbol: Pa Atomic number: 91 Atomic weight: (231) Radioactive metallic element, belongs to the actinoids. The most stable isotope, Pa 231 has a half life of 2.43*10^4 years. At least 10 other radioactive isotopes are known. No practical… …   Elements of periodic system

  • protactinium — [prō΄tak tin′ē əm] n. [ModL: see PROTO & ACTINIUM] a rare, radioactive, metallic chemical element, one of the actinides, found in pitchblende: symbol, Pa; at. no., 91: see the periodic table of elements in the Reference Supplement …   English World dictionary

  • Protactinium — thorium ← protactinium → uranium Pr ↑ Pa ↓ …   Wikipedia

  • Protactinium — Eigenschaften …   Deutsch Wikipedia

  • Protactinium — Prot|ac|ti|ni|um auch: Pro|tac|ti|ni|um 〈n.; s; unz.; chem. 〉 radioaktives chem. Element, Ordnungszahl 91 [<grch. protos „erster, Ur...“ + Actinium] * * * Prot|ac|ti|ni|um [↑ proto u. ↑ Actinium (weil Letzteres aus P. entsteht)], das; s;… …   Universal-Lexikon

  • protactinium — protaktinis statusas T sritis chemija apibrėžtis Cheminis elementas. simbolis( iai) Pa atitikmenys: lot. protactinium angl. protactinium rus. протактиний …   Chemijos terminų aiškinamasis žodynas

  • protactinium — protaktinis statusas T sritis fizika atitikmenys: angl. protactinium vok. Protaktinium, n rus. протактиний, m pranc. protactinium, m …   Fizikos terminų žodynas

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