Measurement and normalization of the relative 239Pu fission cross-section in the low resonance region

Abstract

Measurements of the 239Pu fission cross-section were performed at a well-collimated short flight-path of the C.B.N.M. Linac from 30 eV to below thermal energy for a direct normalization to the 2200 m/s 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 239Pu- 10B-layer. From the counting-rate ratios σ f -curves were calculated assuming a 1/v behaviour of the 10B(n, α) 7Li cross-section. Several fission and resonance integrals are calculated from the normalized σ f -curve and compared with other published results. It is shown that the large discrepancies between the reported results (up to more than a factor of 2) can be considerably reduced by applying a common normalization procedure, e.g. to the fission integral ∫ 9ev 20ev σ f(E)d E=1046·6±10·4 barn ev obtained from these measurements.