Measurement and Normalization of the Relative Uranium-233 Fission Cross Section in the Low Resonance Region

The ²³³U fission cross section was measured at a well-collimated short flight path of the CBNM Linac from 50 eV to below thermal energy for a direct normalization to the 2200 m/sec reference cross section. The fission reaction rate and the neutron spectrum were determined simultaneously with solid state detectors placed on each side of a back-to-back ²³³U-¹⁰B layer. From the counting-rate ratios σ_ƒ curves were calculated assuming a 1/ behavior of the ¹⁰B(n,α)⁷ Li cross section. Several fission and resonance integrals were calculated from the normalized σ_ƒ curve and compared with other published results. Moreover, the Westcott g_ƒ factor was calculated from our data in order to check the shape of the fission cross section below 1 eV. Furthermore, we propose a common normalization procedure based on the fission integral obtained from our measurements.