g boson and systematics of the M1 scissors mode

We discuss systematics of the M1 scissors mode within the interacting boson model when the g-boson degree of freedom is included explicitly and microscopically motivated choices of model parameters are adopted. We try to relate the M1 centroid energy to the energetics of deformation. We conclude that, with the introduction of a hexadecapole-hexadecapole interaction and a g-boson admixture in the ground state of only a few percent, we can obtain reasonable estimates of the M1 centroid energy, without invoking a Majorana interaction. If one takes seriously variations in microscopic estimates of boson g factors, then the summed M1 strength near midshell can be interpreted in terms of boson occupation numbers which saturate. copyright 1996 The American Physical Society