noun

• 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.’

  More example sentences

  • ‘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.’