F spin as a partial symmetry

We use the empirical evidence that F-spin multiplets exist in nuclei for only selected states as an indication that F spin can be regarded as a partial symmetry. We show that there is a class of non-[Formula Presented]-scalar IBM-2 Hamiltonians with partial F-spin symmetry, which reproduce the known systematics of collective bands in nuclei. These Hamiltonians predict that the scissors states have good F-spin and form F-spin multiplets, which is supported by the existing data.