Single-Level Analysis of the Uranium-233 Fission Cross Section for Neutron Energies Between 6 and 124 eV

The fission cross section of ²³³U, measured at liquid nitrogen temperature, has been analyzed between 6 and 124 eV by a single-level formalism. The resonance parameters E, Γ, and σ0Γƒ are presented. These parameters are shown to represent the measured cross section quite well provided that, in addition to the 136 well-resolved resonances, 33 somewhat broad levels (Γ > 500 meV) are added in the vicinity of some of the highly asymmetric resonances. The distributions of the nearest neighbor level spacings are compared with the Wigner distributions. The fission widths, Γƒ, have also been derived for only well-resolved resonances, using a constant value of the radiation width, Γγ = 39 meV. The distribution of these widths compares favorably with a X² distribution with v = 3 degrees-of-freedom.