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Medical Term:


Pronunciation: pro'tak-tin'e-um

Definition: A radioactive element, atomic no. 91, atomic wt. 231.03588, formed in the decay of uranium and thorium; its most long-lived isotope, 231Pa, has a half-life of 32,500 years.

Synonym(s): proactinium, protoactinium

[G. protos, first]

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