Extension of the pairing plus quadrupole force model to N≈Z nuclei

The pairing plus quadrupole force model is extended so as to be applicable to N approximate to Z nuclei. We obtain an isospin-invariant pairing plus quadrupole-quadrupole plus quadrupole pairing interaction accompanied by a isoscalar proton-neutron force. This interaction includes isoscalar and isovector proton-neutron interactions. It is shown that a J-independent isoscalar proton-neutron force plays an essential role in reproducing the nuclear binding energy and roughly degenerate low-lying states, with T=1 and T=0 being observed in N=Z odd-odd nuclei. Numerical calculations compared with experimental data show that the functional interaction with four force parameters is useful in describing both energy levels and binding energies in N approximate to Z nuclei. [S0556-2813(99)05403-5].