Measurement and normalization of the relative ²³⁵U fission cross-section in the low resonance region

Measurements were performed with the Linac of the C.B.N.M. to below thermal energy for a direct normalization of fission cross-sections to the 2200 m/sec reference cross-section. The measurements were performed at a well-collimated short flight-path with low repetition-rate and long burst-width of the Linac. The fission reaction rate and the neutron spectrum were determined simultaneously with solid state detectors on each side of a back-to-back ²³⁵U and ¹⁰B layer. From the counting-rate ratios σ_f-curves were calculated assuming a 1 ν behaviour of the ¹⁰B(n, α⁷Li cross-section. Several fission integrals are calculated from the normalized σ_f curve and compared with other published results. It is shown that the large discrepancies (up to 35 per cent) which exist between the different results can be considerably reduced by a common normalization procedure e.g. using the fission integral ^11eV_7·8eVσf(E)dE=240.2±2.1 barn eV obtained from this measurement.