High resolution neutron total cross section measurement of 89Y

Results of a high resolution neutron time-of-flight experiment for neutron energies 27 < or = E < or = 240 keV on the target nucleus 89Y (J/sup π/-) are presented. The measurement employed a 5 nsec beam burst and a 250 m flight path. A multilevel shape analysis of the data was carried out. The parities of almost all observed resonances were easily determined, and for s wave levels the J values of most resonances were obtained. It was found that the ΣGAMMA0/sub n/ vs E plot of the l = 0, J = 1 levels exhibited a significant change in slope over the 240 keV interval, which was interpreted as evidence for a 1- doorway state. The analysis yielded an escape width GAMMA/sup arrow-up/keV and a spreading width GAMMA/sup arrow-down/keV, with the doorway state located at a neutron energy of 70 keV. No effect attributable to nonstatistical behavior was observed in the p wave channel. Since most s and p wave levels were observed a relatively clean test could be made of the expected ratio of s to p wave level spacings. After estimating the number of missed levels (inferred through the use of the Porter-Thomas distribution), the experimental ratio of s to p wave spacings was found to be 2.74. This is in disagreement with the theoretical level density prediction of 2.06. The average s,p strength functions and level spacings are S0 = 0.28 +- 0.05 x 10-4, S1 = 2.64 +- 0.03 x 10-4, /sub l/ = 4.0 keV, /sub l/ = 1.46 keV