Precision Mass Measurement of $^{58-63}$Cr: Nuclear Collectivity towards the \emph{N}=40 Island of Inversion

TL;DR

This study measured the masses of neutron-rich chromium isotopes with unprecedented precision, revealing insights into nuclear structure and deformation near the N=40 island of inversion, supported by various theoretical models.

Contribution

First mass measurements of $^{58-63}$Cr isotopes at ISOLDE, providing new data that challenge existing nuclear models and support the onset of deformation near N=40.

Findings

Masses are up to 300 times more precise than previous data.

Evidence of gradual deformation onset in Cr isotopes.

Comparison with multiple theoretical models including ab initio calculations.

Abstract

The neutron-rich isotopes $^{58-63}$Cr were produced for the first time at the ISOLDE facility and their masses were measured with the ISOLTRAP spectrometer. The new values are up to 300 times more precise than those in the literature and indicate significantly different nuclear structure from the new mass-surface trend. A gradual onset of deformation is found in this proton and neutron mid-shell region, which is a gateway to the second island of inversion around \emph{N}=40. In addition to comparisons with density-functional theory and large-scale shell-model calculations, we present predictions from the valence-space formulation of the \emph{ab initio} in-medium similarity renormalization group, the first such results for open-shell chromium isotopes.