Definition of protactinium in English:



(also Pa)
  • 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.

    ‘Along the way, these disintegration series produce radioactive isotopes of protactinium, thorium, actinium, radium, francium, radon, astatine, polonium, bismuth, lead, thallium and mercury.’
    • ‘A new method of radioactive tracing involves the use of a new clock, based on the radioactive decay of uranium - 235 to protactinium - 231.’
    • ‘The dates of discovery of these elements as 1789 for uranium, 1829 for thorium, 1899 for actinium and 1913 for protactinium.’
    • ‘All isotopes of protactinium are radioactive.’
    • ‘A protactinium - 234 atom has 91 protons and 143 neutrons.’



/ˌprōtakˈtinēəm/ /ˌproʊtækˈtɪniəm/


Early 20th century from proto-‘original, earlier’ + actinium, so named because one of its isotopes decays to form actinium.