Multi-neutron-hole and core-excited configurations ofisomeric states near the doubly-magic 208Pb

The region of the nuclear chart with atomic number Z = 80-83 (Hg-Bi) and neutron number N = 118-126, which is the subject of many recent investigations, has revealed the presence of quite long-lived states at high excitation energy and spin. Some noteworthy results include the 8-ms, spin (51/2) isomer at about 8 MeV in Bi-205, and the 60-ns, spin 28 level at 13.67 MeV in Pb-208. The states in Bi-205 and Pb-208 have the longest half-life and the highest excitation energy of isomers above 7 MeV identified across the nuclear chart yet. The recently discovered isomers are exceptional in terms of half-life, excitation energy or spin, and are built on excitations of the Pb-208 core, which is the heaviest doubly-magic nucleus. The properties of these isomers with multi-quasiparticle configurations, involving nucleons in predominantly high-j orbitals below and above the Z = 82 and N = 126 shell gaps, are challenging to reproduce through large-scale shell-model calculations owing to the constraints imposed by the large model space. These metastable states constitute the means to discriminate between and serve to improve the available nuclear effective interactions.