Long standing problem of {sup 210}Bi and the realistic proton-neutron effective interaction
The odd-odd nucleus {sup 210}Bi 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 {pi}h{sub 9/2}{nu}g{sub 9/2} are remarkably well reproduced by the theory, which accounts for the 1{sup -} state being the ground state instead of the 0{sup -} predicted by the Nordheim strong coupling rule. It is shown that the core-polarization effects are crucial to produce this inversion. The similarity between proton-neutron multiplets in the {sup 132}Sn and {sup 208}Pb regions is discussed in connection with the effective interaction.