Neutron-proton weak coupling: Reducing shell-model dimensions by truncations in the neutron and proton subspaces

Abstract

A scheme for shell-model truncations based on diagonalizing and then truncating the separate neutron and proton subspaces and then combining the truncated subspaces together for rediagonalization is described and evaluated. Projected m-scheme techniques are used for these calculations and aspects of this technique relevant to this application are discussed. Detailed calculations are made for ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$. The truncated results for level schemes, B(E2) values, and wave-function amplitude distributions are compared with the results of calculations in the analogous full shell-model basis spaces. The results suggest that the neutron-proton ‘‘weak-coupling’’ approach may be an effective truncation scheme even though it is known that the n-p interaction has a dominating influence on these nuclei.