(1) All isotopes of protactinium are radioactive.(2) A protactinium - 234 atom has 91 protons and 143 neutrons.(3) Along the way, these disintegration series produce radioactive isotopes of protactinium , thorium, actinium, radium, francium, radon, astatine, polonium, bismuth, lead, thallium and mercury.(4) The dates of discovery of these elements as 1789 for uranium, 1829 for thorium, 1899 for actinium and 1913 for protactinium .(5) A new method of radioactive tracing involves the use of a new clock, based on the radioactive decay of uranium - 235 to protactinium - 231.
