Magnetic dipole excitation mode according to the collective model with separate neutron and proton deformations

The collective model with separate neutron and proton deformations is developed. The collective motion of individual neutron and proton surfaces is reduced to the motion of the mass surface and the neutron skin. The strong coupling scheme of the neutron skin vibrations to the mass-surface motion is applied for well-deformed nuclei. The magnetic dipole excitation mode, which was discovered experimentally, is explained as the K=1 one-phonon neutron skin vibration in a deformed nucleus. Some estimates of parameters of the model are performed. Finally, the model is confronted with the two-rotor model and the interacting boson model (IBM-2). (orig.)