THE F-SPIN STRUCTURE OF THE NEUTRON-PROTON INTERACTING BOSON MODEL: HAMILTONIAN AND ELECTROMAGNETIC OPERATORS

Abstract

We study the F-spin structure of a general proton-neutron interacting boson model Hamiltonian and of the corresponding electromagnetic operators, using a separation into parts which are symmetric and antisymmetric under the interchange of proton and neutron degrees of freedom. We also use a formal procedure in which we couple proton and neutron operators to a given F-tensor rank. We deduce conditions of F-spin symmetry and F-spin invariance for the Hamiltonian, as well as selection rules for electromagnetic transition matrix elements. We use first order perturbation theory to obtain the (F, Fz)-dependence of the energy and wave functions, when F-vector and F-tensor (rank 2) parts are added to an “unperturbed” Hamiltonian, which is F-spin invariant.