Particle-rotor versus particle-vibration features in g factors of Cd 111 and Cd 113

The emergence and evolution of collective excitations in complex nuclei remains a central problem in the quest to understand the nuclear many-body problem. Nuclear quadrupole collectivity is usually investigated via electric quadrupole observables. Here, however, we measure the g factors of low-excitation states in Cd111 and Cd113 and show that they are sensitive to the nature of the collectivity in these nuclei in ways that the electric quadrupole observables are not. The particle-vibration model, which assumes spherical core excitations, cannot explain the g factors, whereas a particle-rotor model with a small, nonzero core deformation does. The contrast of the two models is made stark by the fact that they begin from the same limiting g-factor values: It is shown that when an odd nucleon occupies a spherical orbit with angular momentum j=1/2, or a deformed orbit with j=1/2 parentage, the particle-vibration model and the particle-rotor model both reduce to the same g-factor value in their respective limits of zero particle-vibration coupling or zero deformation.