text: The 4n chain of thorium-232 is commonly called the "thorium series" or "thorium cascade". Beginning with naturally occurring thorium-232, this series includes the following elements:  actinium, bismuth, lead, polonium, radium, radon and thallium.  All are present, at least transiently, in any natural thorium-containing sample, whether metal, compound, or mineral. The series terminates with lead-208.
  Plutonium-244 (which appears several steps above thorium-232 in this chain if one extends it to the transuranics) was present in the early Solar System, and is just long-lived enough that it should still survive in trace quantities today, though it is uncertain if it has been detected.
  The total energy released from thorium-232 to lead-208, including the energy lost to neutrinos, is 42.6 MeV.