The isospin-dependent quadrupole-quadrupole interaction used in shell model calculations – the effects of including ΔN = 2 excitations and a two-body spin-orbit interaction term

Abstract

The effect of the "B" term in the interaction −χQ(1) · Q(2)[1 + Bτ (1) · τ (2)] was previously considered in the 0p shell (small space). It is now studied in a larger space which additionally includes ∆N = 2 excitations. When B is made sufficiently negative we still obtain for 10 Be, even in the larger space, an unphysical collapse of some of the low-lying states so that their energies are less than the energy of the conventional J = 0 + ground state. This effect, however, occurs for values of B considerably more negative than was the case in the smaller space. It is shown that the inclusion of an additional two-body spin-orbit interaction term prevents this unrealistic collapse in both the large and small spaces.