Identification of a new isomeric state in ⁷⁶Zn following the β decay of ⁷⁶Cu

Shell evolution far from stability can be explored by measuring the properties of isomeric states, which provide a sensitive probe of the microscopic structure of the nucleus. Beta decay is an attractive method for isomer identification because daughter nuclei can be populated in an excited state which subsequently decays to the ground state through one or more isomeric transitions. A β-decay experiment was recently performed at the National Superconducting Cyclotron Laboratory (NSCL) to identify and study isomeric states in the vicinity of the doubly magic nucleus ⁷⁸Ni. Radioactive ions produced by beam fragmentation at the NSCL's Coupled Cyclotron Facility were implanted into a CeBr₃ scintillator detector coupled to a position-sensitive photomultiplier tube (PSPMT). Ancillary arrays of HPGe clover and LaBr₃ detectors were positioned around the implantation detector to measure β-delayed γ rays. The entire suite of detectors was instrumented with the NSCL Digital Data Acquisition System (DDAS). Dynode traces recorded by DDAS were analyzed to selectively identify isomeric transitions. The previously observed 2634-keV level in ⁷⁶Zn, populated following the β decay of ⁷⁶Cu, was identified as isomeric with a half-life of 25.4(4) ns. A combination of timing and γ-ray spectroscopy was used to confirm this assignment. Shell-model calculations were performed which indicate that this state may be a high-spin negative-parity state formed by the occupation of the neutron 0g_9/2 orbital. The experimental results and theoretical interpretation will be presented.