Spin-aligned neutron-proton pairs in $N=Z$ nuclei

TL;DR

This paper investigates the significance of spin-aligned neutron-proton pairs with J=9 in the low-energy spectra of N=Z nuclei, using shell-model calculations and boson mapping to understand their role and limitations.

Contribution

It introduces an analysis of aligned neutron-proton pairs in N=Z nuclei using shell-model and boson mapping, highlighting their strengths and limitations.

Findings

Aligned J=9 neutron-proton pairs are significant in low-energy spectra.

The analysis identifies strengths and deficiencies of the aligned-pair approximation.

Shell-model and boson mapping provide complementary insights.

Abstract

A study is carried out of the role of the aligned neutron-proton pair with angular momentum J=9 and isospin T=0 in the low-energy spectroscopy of the $N=Z$ nuclei $^{96}$Cd, $^{94}$Ag, and $^{92}$Pd. Shell-model wave functions resulting from realistic interactions are analyzed in terms of a variety of two-nucleon pairs corresponding to different choices of their coupled angular momentum $J$ and isospin $T$. The analysis is performed exactly for four holes ($^{96}$Cd) and carried further for six and eight holes ($^{94}$Ag and $^{92}$Pd) by means of a mapping to an appropriate version of the interacting boson model. The study allows the identification of the strengths and deficiencies of the aligned-pair approximation.