is also formed in this process, via (n,2n) reactions between fast neutrons and , , and :
Unlike most even numbered heavy isotopes,  is also a fissile fuel fissioning just over half the time when it absorbs a thermal neutron.  has a relatively short half-life (), and some decay products emit high energy gamma radiation, such as ,  and particularly . The full decay chain, along with half-lives and relevant gamma energies, is:
 decays to  where it joins the decay chain of 
Thorium-cycle fuels produce hard gamma emissions, which damage electronics, limiting their use in bombs.  cannot be chemically separated from  from used nuclear fuel; however, chemical separation of thorium from uranium removes the decay product  and the radiation from the rest of the decay chain, which gradually build up as  reaccumulates. The contamination could also be avoided by using a molten-salt breeder reactor and separating the  before it decays into .  The hard gamma emissions also create a radiological hazard which requires remote handling during reprocessing.