IBA-1 as a model of IBA-2

Eigenstates of a realistic IBA-2 hamiltonian which gives a very good description of the 178Hf spectrum are rather far from having definite F-spins. Still, this IBA-2 hamiltonian projected on the set of states with maximum symmetry, F=Fsub(max)=15/2, yields spacing between low-lying levels in good agreement with the exact ones. Slight modifications of the parameters in the projected hamiltonian thus obtained yield a simple IBA-1 hamiltonian which is a very good model of the more detailed IBA-2 hamiltonian. (orig.)