Angular Distributions of Gamma Rays Produced in theY89(n,n′γ)Y89Reaction

The differential cross sections for the production of $\gamma$ rays from the ${\mathrm{Y}}^{89}(n,n^{\prime }\gamma ){\mathrm{Y}}^{89}$ reaction have been measured at incident neutron energies of 3.0, 3.25, 3.5, 4.0, 4.1, and 4.5 MeV. At the highest incident neutron energy, $\gamma$ rays with energies of 0.71, 0.908, 1.31, 1.51, 1.62, 1.75, 1.95, 1.98, 2.10, 2.46, 2.58, 2.70, 2.86, 3.09, 3.49, and 3.85 MeV have been observed. Angular distribution of these $\gamma$ rays have been measured at neutron energies of 3.25 and 4.0 MeV. The distributions have also been calculated theoretically on the basis of the Satchler formalism using the computer program TRANSEC developed at this laboratory. A comparison between the experimental and theoretical cross sections has led to spin assignments for the 1.51-, 1.75-, 2.22-, 2.53-, 2.86-, 3.09-, and 3.49-MeV levels in the ${\mathrm{Y}}^{89}$ nucleus. The $\gamma$-ray spectra indicate the existence of an excited level at 3.85 MeV.