In-beam $\gamma-$spectroscopy of the transitional nucleus $^{217}$Ac

TL;DR

This study investigates high-spin states in the transitional nucleus $^{217}$Ac using in-beam gamma spectroscopy, revising the level scheme, establishing new states, and comparing experimental results with shell-model calculations.

Contribution

It provides the first detailed level scheme above the 29/2$^+$ isomer and compares experimental data with shell-model predictions, resolving previous inconsistencies.

Findings

Established high-spin states up to 3.8 MeV and 41/2$^+$.

Revised and confirmed the level scheme below 29/2$^+$.

Compared experimental levels with shell-model calculations, supporting weak coupling interpretation.

Abstract

High-spin states in the transitional $^{217}$Ac nucleus are established up to 3.8 MeV excitation energy and $I^{\pi} =$ 41/2$^+$ with the addition of around 20 new transitions. The structure of the yrast and near-yrast states below the 29/2$^+$ isomer is revisited. The inconsistencies in the level schemes reported earlier are resolved. The level structure above the 29/2$^+$ isomer is established for the first time. Large-basis shell-model calculations with the KHPE interaction are performed to compare the experimentally observed level energies with the theoretical predictions. A comparison with the systematics of the N = 128 isotones suggests that the yrast structures result from a weak coupling of the odd proton to the even-even 216Ra core, which is consistent with the shell-model configurations. Furthermore, alpha decay of the 29/2$^+$ isomer is revisited and the decay scheme established from this work is discussed in the framework of the shell model.