Systematics of 2+ states in semi-magic nuclei

TL;DR

This paper develops a simple model using QRPA to systematically analyze low-lying 2+ energy levels and electromagnetic transitions in semi-magic nuclei, accurately matching experimental data and highlighting the role of nucleons in closed shells.

Contribution

It introduces a straightforward relation linking 2+ energies with pairing and quadrupole interactions, providing a unified description across multiple semi-magic isotopic and isotonic chains.

Findings

Model accurately reproduces experimental energy levels and B(E2) values.

Both active and closed-shell nucleons significantly influence nuclear excitations.

The simple relation offers a practical tool for nuclear structure analysis.

Abstract

We propose a simple systematics of low lying 2+ energy levels and electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase Approximation (QRPA). We derive a simple relation connecting the 2+ energy with the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns out that the systematics of energy levels and B(E2) values predicted by this simple model is fulfilled with a reasonable accuracy by all available experimental data. Both systematics suggest that not only active nucleons but also those filling closed shells play an important role.