First observation of a shape isomer and a low-lying strongly-coupled prolate band in neutron-deficient semi-magic 187Pb

Prompt and delayed γ-ray spectroscopy of the neutron-deficient, semi-magic isotope 187Pb has been performed using recoil-decay isomer-decay tagging techniques at Argonne Gas-Filled Analyzer. A new 5.15(15)-μs isomeric state only 308 keV above spherical 3/2− ground is identified classified as a shape isomer. strongly-coupled band observed on top isomer, which nearly identical to one built prolate 7/2−[514] Nilsson in isotone 185Hg. Based this similarity result potential-energy surface calculations, isomer proposed originate from same configuration. The retarded character 308-keV (7/2−)→3/2gs− transition with deduced B(E2)=5.6(2)×10−4 W.u. can be well explained by significant difference between parent daughter configurations, leading isomerism. excitation energy surprisingly low, being roughly half energies known 0+ intruder bandheads neighboring 186,188Pb isotopes. combined results present work previous α-decay laser studies evidence for triple coexistence low negative-parity configurations 187Pb, reproduced calculations.