Neutron resonance parameters of 238U

Abstract

Neutron transmission measurements on natural uranium samples were performed in the energy region from 20 eV up to 4.7 keV on a 190 m flight path of the JAERI 120 MeV linac neutron time-of-flight spectrometer. Samples were all metallic slabs with three thicknesses of 0.00725, 0.0144 and 0.0236 atoms/barn, respectively. One of them was cooled down to 77 K to reduce Doppler broadening effect. The best nominal resolution of the measurements was 0.3 ns/m. Special attention has been paid to background determination, because its shape was found to depend on the thickness of the sample in the beam. Resonance parameters Γ ∘ n are obtained for 180 resonances in the energy region up to 4.7 keV with the Atta-Harvey area-analysis programme. Excluding p-wave resonances assigned by Corvi et al., the average level spacing, the average reduced neutron width and the strength function were determined to be D ̄ = 21.9 eV , Γ ∘ n = 2.47 ± 0.33 meV and S 0 = (1.13 ± 0.13) × 10 −4, respectively. The statistics of the level spacings are in agreement with those predicted by the theory of Dyson and Mehta and are inconsistent with an uncorrelated Wigner distribution. Results are compared with currently available experimental data.