Nuclear-Structure Studies ofSr88andY89by Inelastic Alpha-Particle Scattering

Abstract

The inelastic scattering of 42-MeV alpha particles from ${\mathrm{Sr}}^{88}$ and ${\mathrm{Y}}^8$, was studied in order to test the validity of the weak-coupling core-excitation model for these nuclei and to obtain an angular distribution for the excitation of the $g_{\frac{9}{2}}$ single-particle state at 0.906 MeV in ${\mathrm{Y}}^{89}$. Angular distributions were obtained for scattering to the ground state and the 1.84-MeV ($2^{+}$), 2.74-MeV ($3^{-}$), and 3.21-MeV ($2^{+}$) states in ${\mathrm{Sr}}^{88}$; and to the ground state and the 0.906-MeV (${\frac{9}{2}}^{+}$), 1.51-MeV (${\frac{3}{2}}^{-}$), 1.75-MeV (${\frac{5}{2}}^{-}$), 2.22-MeV (${\frac{5}{2}}^{+}$), 2.53-MeV (${\frac{7}{2}}^{+}$), 2.84-MeV, and 3.1-MeV states in ${\mathrm{Y}}^{89}$. The phase rule was used to obtain parities for additional levels in ${\mathrm{Y}}^{89}$ at 3.70, 3.98, and 4.17 MeV. A parametrized phase-shift analysis was used to fit the elastic-scattering data, and the Austern-Blair model with the same parameters was used to extract values of ${\beta }_{I}R$ from the inelastic angular distributions. It is shown that the weak-coupling model is not a good description for the excited states of ${\mathrm{Y}}^{89}$. A shell-model calculation correlating the differential cross sections to the $2^{+}$ states in ${\mathrm{Sr}}^{88}$ and the 1.51- and 1.75-MeV states in ${\mathrm{Y}}^{89}$ is made, and the results are found to be in slightly better agreement with experiment. The differential cross section to the 0.906-MeV ($g_{\frac{9}{2}}$) single-particle state is in agreement with the Austern-Blair model for an $I=5\mathrm{}$ transition.