Coherence features of the spin-aligned neutron-proton pair coupling scheme

TL;DR

This paper explores a new coupling mode in N=Z nuclei, showing that spin-aligned neutron-proton pairs significantly influence the structure of certain nuclear states, challenging traditional seniority-based classifications.

Contribution

It introduces the concept of isoscalar spin-aligned np pair mode and demonstrates its relevance in describing the ground and low-lying states of specific N=Z nuclei using shell model calculations.

Findings

Ground and low-lying states of 92Pd and 96Cd are mainly built on spin-aligned np pairs.

These pairs carry maximum angular momentum J=9 in the 0g9/2 shell.

The np interaction favors this new coupling mode over seniority schemes.

Abstract

The seniority scheme has been shown to be extremely useful for the classification of nuclear states in semi-magic nuclei. The neutron-proton ($np$) correlation breaks the seniority symmetry in a major way. As a result, the corresponding wave function is a mixture of many components with different seniority quantum numbers. In this contribution we show that the $np$ interaction may favor a new kind of coupling in $N=Z$ nuclei, i.e., the so-called isoscalar spin-aligned $np$ pair mode. Shell model calculations reveal that the ground and low-lying yrast states of the $N = Z$ nuclei $^{92}$Pd and $^{96}$Cd may mainly be built upon such spin-aligned $np$ pairs each carrying the maximum angular momentum $J = 9$ allowed by the shell $0g_{9/2}$ which is dominant in this nuclear region.