Resonance Capture of Neutrons by Uranium

Abstract

The resonance capture of slow neutrons by ${\mathrm{U}}^{238}$ has been studied by absorption methods with good geometry and thin detectors using the cyclotron as an intense source of neutrons. The experimental cross section for self-absorption for slow neutrons transmitted by cadmium was measured with thin absorbers and found to be 4600\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$/atom\ifmmode\pm\else\textpm\fi{}40 percent. Evidence is given for the existence of more than one level. The predominant level has an energy somewhat under 11 ev, a total natural width somewhat less than 0.20 ev and a neutron width somewhat less than 0.0086 ev. The value $\ensuremath{\int}\frac{\ensuremath{\sigma}\mathrm{dE}}{E}$ in the resonance region was found to be 290\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$/atom\ifmmode\pm\else\textpm\fi{}40 percent.