Isospin asymmetries in pion scattering to isoscalar giant quadrupole states in Ni isotopes

Inelastic scattering of 180 MeV ${\pi }^{\mathrm{-}}$ and ${\pi }^{+}$ from ${}_{}{}^{58}{}_{}{}^{}$,60,62,64Ni shows a prominent quadrupole feature near 65$A^{\mathrm{-}1/3}$ MeV, identified as the familiar isoscalar giant quadrupole resonance. For the heavier two isotopes, the ${\pi }^{\mathrm{-}}$ scattering cross sections greatly exceed those for ${\pi }^{+}$, the same effect previously noted in pion scattering on heavy nuclei. Since these four nickel targets contain a range of single-nucleon binding energies, these new data demonstrate the influence of these single-particle effects on the apparent isospin response, increasingly neutronlike for the heavier isotopes.