CollectiveM1 states in the classical limit of the neutron-proton interacting boson model

Abstract
Using the classical picture of the collective M1 mode in nuclei as an oscillation of the angle between the deformed valence protons and valence neutrons, we obtain an expression for the classical limit of the neutron-proton interacting boson model Hamiltonian. We use this result to contrast the excitation energy in the classical limit to the experimentally observed value for the 1sup+ state in sup156Gd.