89Y + n resonances for E = 10–740 keV and intermediate structure

Abstract High-resolution neutron total-cross-section measurements on 89 Y have been made from a few eV to 1 MeV using the pulsed neutron time-of-flight spectroscopy at ORELA with a neutron burst width of 5 ns and a nominal resolution of 0.025 ns/m at the highest energy. We have analyzed the data from 10–740 keV using a multilevel R -matrix code and obtained the values of resonance parameters ( E 0 , J π , g Γ n ). From these results we have obtained the values of average quantities up to about 600 keV: D l = 0 = 4.6 ± 0.3 keV, D l = 1 = 1.35 ± 0.15 keV; S 0 = 0.33 ± 0.045, S 1 = 5.82 ± 0.38, in units of 10 −4 eV − 1 2 . The staircase plots of reduced neutron widths for s- and p-waves and the plots of the Lorentz-weighted strength functions averaged over different energy intervals show an evidence of several doorway states. A least-squares fit to the lorentzian smooth curves provides the best values of E d (doorway energy) and γ 2 d c (escape reduced width of doorway). These values are in qualitative agreement with the theoretical predictions. The experimental ratio of s- to p-wave level spacings was found to be 3.43 ± 0.6. This is in disagreement with the theoretical prediction of 2.06 (for σ = 3.8) and indicates a parity dependence of the level density at high excitation.