Pion scattering to collective excitations in 90Zr and 118Sn.

Abstract

Inelastic scattering of 163 MeV ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ and ${\ensuremath{\pi}}^{+}$ 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 ${3}^{\mathrm{\ensuremath{-}}}$ 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 ${3}^{\mathrm{\ensuremath{-}}}$ 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 ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ than ${\ensuremath{\pi}}^{+}$ strength, while the low-energy octupole resonance is excited symmetrically.