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

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 ${\hat{I}}^3$ 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.

PRC accepted