2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/191711The odd-odd nucleus 210Bi is studied within the framework of the shell model using effective two-body matrix elements derived from the CD-Bonn nucleon-nucleon potential. The experimental energies of the proton-neutron multiplet ph9/2 ng9/2 are remarkably well reproduced by the theory, which accounts for the 1- state being the ground state instead of the 0- predicted by the Nordheim strong coupling rule. It is shown that the core-polarization effects are crucial to produce this inversion. The similarity between neutron-proton multiplets in the 132Sn and 208Pb regions is discussed in connection with the effective interaction.4 pages, 3 figures, 1 table, to be published on Physical Review C as a Rapid CommunicationNuclear Theorytext