Isomeric states in neutron-rich nuclei around $N = 40$

TL;DR

This study investigates isomeric states in neutron-rich nuclei around N=40, revealing new isomers and measuring their lifetimes, which enhances understanding of shell evolution and deformation in this region.

Contribution

The paper reports the discovery of a new isomer in $^{58}$Sc and the first lifetime measurement of an isomer in $^{64}$V, providing new insights into nuclear structure near N=40.

Findings

Discovery of a new isomer in $^{58}$Sc.

First lifetime measurement of an isomer in $^{64}$V.

Evidence of parity-changing transitions related to the $1g_{9/2}$ orbital.

Abstract

Neutron-rich nuclei in the vicinity of the $N=40$ island of inversion are characterized by shell evolution and exhibit deformed ground states. In several nuclei isomeric states have been observed and attributed to excitations to the intruder neutron $1g_{9/2}$ orbital. In the present study we searched for isomeric states in nuclei around $N=40$, $Z=22$ produced by projectile fragmentation at RIBF. Delayed $\gamma$ rays were detected by the EURICA germanium detector array. High statistics data allowed for an updated decay scheme of $^{60}$V. The lifetime of an isomeric state in $^{64}$V was measured for the first time in the present experiment. A previously unobserved isomeric state was discovered in $^{58}$Sc. The measured lifetime suggests a parity changing transition, originating from an odd number of neutrons in the $1g_{9/2}$ orbital. The nature of the isomeric state in $^{58}$Sc is thus different from isomers in the less exotic V and Sc nuclei.