Pion scattering to collective excitations inZr90andSn118

Inelastic scattering of 163 MeV ${\pi }^{\mathrm{-}}$ and ${\pi }^{+}$ to the collective states of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$ was used to determine the neutron-proton composition of the transitions. The lowest $2^{+}$ and $3^{\mathrm{-}}$ states were examined for both targets, as were the low-energy octupole, giant quadrupole, and giant monopole excitations. Only slight deviations from the features expected for a hydrodynamic model are observed for the low-lying $3^{\mathrm{-}}$ and $2^{+}$ states of ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$, but these states are observed to be proton-like in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. The giant quadrupole resonances and giant monopole resonances in both targets show a significantly greater ${\pi }^{\mathrm{-}}$ than ${\pi }^{+}$ strength, while the low-energy octupole resonance is excited symmetrically.