Consistent description of magnetic dipole properties in transitional nuclei

It is shown that a consistent description of magnetic dipole properties in transitional nuclei can be obtained in the interacting boson model-2 by Fspin breaking mechanism, which is associated with differences between the proton and neutron deformations. In particular, the long standing anomalies observed in the g-factors of the Os-Pt isotopes are resolved by a proper inclusion of F-spin breaking. 21.10Ky, 21.60Fw Typeset using REVTEX 1 The description of magnetic dipole (M1) properties in the interacting boson model (IBM) [1] has had a checkered career (see [2] for a recent review). In the original model (IBM-1 with s and d bosons), the one-body M1 operator, being proportional to the angular momentum, results in vanishing M1 transitions. Thus to explain observed M1 transitions one needs at least a two-body M1 operator [3] whose microscopic origin is not very clear. The discovery of the “scissors” mode [4] has shifted attention to the proton-neutron version of the model (IBM-2) which provides a more natural basis for description of M1 properties via the F spin breaking mechanism. F -spin measures the degree of symmetry between the valence protons and neutrons and its breaking is linked to the difference between the proton and neutron deformations [5]. In this sense, M1 properties provide complimentary information to E2 observables which depend on the average deformation and are, therefore, insensitive to F -spin breaking. In IBM-2, the one-body M1 and magnetic moment operators are given by