Angular distributions for ${\mathrm{\pi }}^{+}$ and ${\mathrm{\pi }}^{\mathrm{-}}$ elastic and inelastic scattering from the Z=28 closed-proton-shell nuclei ${}_{}{}^{58,60,62,64}{}_{}{}^{}\mathrm{Ni}$ have been measured at an incident pion kinetic energy of 180 MeV. Values for the neutron and proton matrix elements for the transition to the ${\mathit{J}}^{\mathrm{\pi }}$=$2_1^{+}$ state have been extracted using the distorted wave impulse approximation in which the ${\mathrm{\pi }}^{+}$ and ${\mathrm{\pi }}^{\mathrm{-}}$ data were fitted simultaneously and the neutron and proton vibrational transition strengths were treated as free parameters. While all transitions are predominantly collective, extracted values of ${\mathit{M}}_{\mathit{n}}$/${\mathit{M}}_{\mathit{p}}$ indicate increasing collectivity as a function of neutron number and are consistent with the collective limit of N/Z for ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$. © 1996 The American Physical Society.

• Received 25 July 1995

DOI:https://doi.org/10.1103/PhysRevC.53.1167