Levels inY89Excited by theY89(n,n′γ)Reaction

Abstract

Gamma-ray spectra from the ${\mathrm{Y}}^{89}(n,n^{\prime }\gamma )$ reaction have been studied using a ring geometry for fifteen ${\mathrm{Li}}^7\mathrm{}(p,n)\mathrm{}$ neutron energies ranging from 0.78 to 3.36 MeV. Ground-state gamma-ray transitions arising from levels in ${\mathrm{Y}}^{89}$ at 0.908±0.003, 1.506±0.005, 1.745±0.006, 2.84±0.02, and 3.05±0.03 MeV, as well as cascade gamma rays of 0.71±0.01, 1.31±0.01, and 1.62±0.01 MeV arising from levels in ${\mathrm{Y}}^{89}$ at 2.22±0.01 and 2.53±0.01 MeV, have been observed. Spin and parity assignments of ${3/2}^{-}$ and ${5/2}^{-}$ have been made for the 1.51- and 1.75-MeV levels, primarily as a result of comparisons of ratios of experimental cross sections for these two levels with theory. Tentative assignments are made for higher levels. Theoretical level excitation cross-section calculations for various values of spin and parity are done with a computer using the Hauser-Feshbach method and optical-model transmission coefficients obtained from various theories. The 1.75-MeV gamma-ray angular distribution was calculated using Satchler's theory and the corresponding level excitation cross section was corrected accordingly.