- protactinium
[protactinium 词源字典]
- "The chemical element of atomic number 91, a radioactive metal of the actinide series, occurring in small amounts as a product of the natural decay of uranium", Early 20th century: from proto- 'original, earlier' + actinium, so named because one of its isotopes decays to form actinium.[protactinium etymology, protactinium origin, 英语词源]