Neutron-Capture Cross Section of Actinium-227

In the production of actinium-227 by thermal neutron irradiation of radium-226, thorium-228 has been recovered as a by-product. The reactions involved are: ${\mathrm{Ra}}^{226}(n, \gamma ){\mathrm{Ra}}^{227}\to {\mathrm{Ac}}^{227}+{\beta }^{-}$, and ${\mathrm{Ac}}^{227}(n, \gamma ){\mathrm{Ac}}^{228}\to {\mathrm{Th}}^{228}+{\beta }^{-}$. The thermal neutron capture cross section of actinium-227 is 495±35 barns, as determined by the pile oscillation method. The half-life of thorium-228, determined by daily alpha counting for two years, is 697.8±0.7 days or 1.910±0.002 year.