Multilevel Analysis of the Slow Neutron Cross Sections ofU233

A multilevel analysis of the slow neutron total and fission cross sections of ${\mathrm{U}}^{233}$ from thermal energies to 11 ev has been carried out, under the assumption that in one of the two spin states the nucleus undergoes fission primarily through a small number of channels. The cases of one and of two fission channels for this spin state have been investigated in detail. Although the analysis does not yield an exact value for the number of available fission channels, the data are adequately fit with a two fission channel formula. It is not necessary to invoke any negative energy resonances in the analysis. The presence of a noninterfering component in the cross sections, having a $\frac{1}{v}$ energy variation, is indicated. At thermal energies, this component accounts for approximately 80% of the total and fission cross sections. An interpretation of this component as being due to one spin state of the compound nucleus is presented. Under this assumption, the fission characteristics of the two spin states of the compound nucleus formed by $s$-wave neutrons are quite different.