Starting from the microscopic low-momentum nucleon-nucleon interaction $V_{\mathrm{low}k}$, we present a systematic shell-model study of magnetic moments and magnetic dipole transition strengths of the basic low-energy one-quadrupole phonon excitations in nearly spherical nuclei. Studying in particular the even-even $N=52$ isotones from ${}^{92}\mathrm{Zr}$ to ${}^{100}\mathrm{Cd}$, we find the predicted evolution of the predominantly proton-neutron nonsymmetric state reveals a restoration of collective proton-neutron mixed-symmetry structure near midshell. This provides a quantitative explanation for the existence of pronounced collective mixed-symmetry structures in weakly collective nuclei.

• Received 7 September 2006

DOI:https://doi.org/10.1103/PhysRevC.76.034325