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Definition of protactinium noun from the Oxford Advanced Learner's Dictionary

protactinium

noun

/ˌprəʊtækˈtɪniəm/

/ˌprəʊtækˈtɪniəm/

[uncountable]

(symbol Pa)

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a chemical element. Protactinium is a radioactive metal found naturally when uranium decays .
Word Originearly 20th cent.: from proto- ‘original, earlier’ + actinium, so named because one of its isotopes decays to form actinium.

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adjective

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