Effective g factors and proton-boson numbers in the vicinity of proton subshell closures

Abstract

New experimental results on g factors of 2 1 + states are analyzed together with existing data in the Ba-Dy region. It is shown that a simple relation, based on constant values of the proton and neutron boson g factors can describe a broad range of nuclei. Moreover, the extracted values yield a much improved description of the B(M1) strengths to the newly discovered collective isovector excitations in the rare earth region. The anomalous values of g(2 1 +) that occur in the region of the Z = 64 subshell closure are then described in terms of changes in the effective number of proton bosons N π eff which take part in the collective motion, and the deduced values of N π eff are compared with recent microscopic calculations. A similar approach is used to predict g(2 1 +) values in the region of the Z = 40 subshell near A = 100.