Nuclear structure with Dirac phenomenology

Abstract

With non-relativistic Bonn A G matrix elements, it appears that the spin-orbit interaction in a nucleus is too small. As a consequence the wave functions in the 0 p shell are too close to the LS limit. The introduction of a Dirac nucleon effective mass m ∗ less than the free mass enhances the spin-orbit interaction and affects nuclear structure in a very significant way. For example, the B(M1) in 12C to the J π = 1 1 +, T = 1 state is increased by a factor of 2.5 when m ∗/m is decreased from 1 to 0.67. In the above analyses, large-space shell-model calculations are essential to prevent collapse of 1 + states below the ground state. A superficial analysis suggests that the tensor interaction in the nucleus is too large despite the small percentage of the D-state admixture for Bonn A (about 4.4%). However, there are some complications in the analysis. It is emphasized that in order to see large effects of the Dirac phenomenology in nuclear structure, it is essential to calculate single-particle energies with the same interaction that is used for the particle-particle matrix elements in the open shell. This also holds for the core polarization corrections.