Resonance Capture of Neutrons by Uranium

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×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom±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 $\int \frac{\sigma \mathrm{dE}}{E}$ in the resonance region was found to be 290×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom±40 percent.