Search for the missing isomer in the rare-earth nucleus ¹⁵⁸Pm

Probing the intrinsic and collective structure of nuclei in the light rare-earth region provides important insight into the evolution of nuclear deformation and the properties of neutron-rich nuclei far from stability. This understanding is critical for exploring the formation of the rare-earth peak in the r-process abundance pattern, where new data can influence constraints on the possible astrophysical sites and conditions. The odd-odd nucleus ¹⁵⁸Pm is a particularly interesting case as a predicted isomeric state has yet to be clearly established. Investigating such isomers is critical to determining their structure as well as to remove ambiguities that can arise in direct mass measurements. To investigate this region a βγ-coincidence experiment was performed at Argonne National Laboratory (ANL) using the HPGe clover detectors of X-Array (XA) combined with the SATURN moving tape system. Radioactive ions produced by the Californium Rare Isotope Breeder Upgrade (CARIBU) facility were isobarically separated and delivered to the XA+SATURN decay station. Various tape cycles were optimized for the decay of a given species, with a focus on ¹⁵⁸Pm and ¹⁶⁰Sm. In this talk, evidence addressing the missing ¹⁵⁸Pm isomer will be presented as well as new β-decay data on the relevant A=158 and 160 isobars.