5 pags., 4 figs., 1 tab.
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.
This experiment was carried out at the RIBF operated by RIKEN Nishina Center, RIKEN, and CNS, University of Tokyo. We would like to thank the RIKEN accelerator and BigRIPS teams for providing the high intensity beams. This work has been supported by JSPS KAKENHI (Grants No. 25247045 and No. 19H00679), by the German BMBF (Grants No. 05P15RDFN1 and No. 05P19RDFN1), by the German DFG (Project No. 279384907-SFB 1245), by the STFC (U.K.), by the Korean National Research Foundation (Grants No. NRF-21A20131111123 and No. NRF2015H1A2A1030275), by NKFIH (Grant No. NN128072), and by the UNKP-20-5-DE-2 New National Excellence Program of the Ministry of Human Capacities of Hungary. K.W. acknowledges support from the Spanish Ministerio de Economía y Competitividad Grant No. RYC-2017-22007. G.K. acknowledges support from the Janos Bolyai Research Fellowship of the Hungarian Academy of Sciences.