F spin as a partial symmetry - art. no. 024305

We use the empirical evidence that F-spin multiplets exist in nuclei for on ly selected states as an indication that F spin can be regarded as a partia l symmetry. We show that there is a class of non-F-scalar IBM-2 Hamiltonian s with partial F-spin symmetry, which reproduce the known systematics of co llective bands in nuclei. These Hamiltonians predict that the scissors stat es have good F-spin and form F-spin multiplets, which is supported by the e xisting data.