Neutron core excitations in the N=126 nuclide Po210

Excited states above the 16+ isomer in Po210 have been identified using time-correlated γ-ray spectroscopy techniques and the Hg204(C13,3nα) Po210 reaction. States up to ~27 have been identified, including an isomer at 8074 keV with a mean life of 13(2) ns. Among the new states, a candidate for the 17+ state obtained from maximal coupling of the π[h9/2i13/2]11- valence proton configuration and the ν[p1/2-1i11/2]6- neutron core excitation has been identified. This and other results are compared with semiempirical shell-model calculations that predict that single core excitations from the i13/2 neutron orbital and double core excitations out of the p1/2 and f5/2 orbitals, populating the g9/2,i11/2, and j15/2 orbitals above the N=126 shell, will compete in energy. Good agreement is obtained for the lower states but there are systematic discrepancies at high spins including the absence of states that are calculated to lie low in the spectrum, implying uncertainties for configurations associated either with the i13/2 neutron hole or double core excitations.