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protactinium n. 鏷 鏷 protactinium n 1: a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead [synonym: {protactinium}, {protoactinium}, {Pa}, {atomic number 91}] Protactinium \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] 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 applications are known. Discovered in 1917 by Lise Meitner and Otto Hahn.
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