Low-Energy Neutron Cross Sections of Fissionable Nuclei

The method of analysis developed in a previous paper is applied to the low-energy neutron cross sections of the common fissionable isotopes. Further evidence is presented to show that ${\mathrm{U}}^{235}$ possesses the unusual negative energy level required by the previous analysis. However, good fits are obtained for the cross sections of both ${\mathrm{U}}^{233}$ and ${\mathrm{Pu}}^{239}$ without such an unusual bound level, suggesting that the neutron resonance cross sections of the fissionable isotopes do not exhibit a basic anomaly. The size of the level interference effects in each of the isotopes implies that the fission process involves more than one but no more than a few fission channels.