  The production of the industrially significant radionuclide polonium-210 from
the neutron irradiation of bismuth metal and the subsequent beta decay of
bismuth-210 is highly inefficient due to the small neutron capture cross
section of bismuth-209. In this paper, we report a previously undescribed
self-sustaining nuclear chain reaction involving self-propagating neutron
multiplication in bismuth salts that allow for rapid and cost-effective
production of polonium- 210. The reaction proceeds in a cycle of three
alternating elementary steps - the capture of neutrons by bismuth-209 and the
subsequent formation of polonium-210, the emission of high-energy alpha
particles by polonium-210, and the production of more neutrons from (alpha,n)
and (n,2n) reactions on light element and bismuth-209 nuclei respectively. The
chain reaction was proven to have successfully occurred by irradiating a sample
of the bismuth salt with a 80 microcurie neutron source and monitoring the
activity levels of the reaction. It was found that the activity of the reaction
increased exponentially after an initial stable period following a derived
formula for polonium production trends for the reaction, thus validating the
occurrence of the reaction. Furthermore, alpha spectroscopy confirmed that
polonium-210 had been produced by characterising the 5.30 MeV alpha emission
peak of the reaction in addition to using beta spectroscopy to identify the
parent nuclide bismuth-210, further proving that the reaction was successful.
