Competition between excited core states and 1hω single-particle excitations at comparable energies in 207Pb from photon scattering

The Pb(γ→,γ') photon scattering reaction has been studied with the nearly monochromatic, linearly polarized photon beams at the High Intensity γ-ray Source (HIγS) at the DFELL. Azimuthal scattering intensity asymmetries measured with respect to the polarization plane of the beam have been used for the first time to assign both the spin and parity quantum numbers of dipole excited states of 206,207,208Pb at excitation energies in the vicinity of 5.5 MeV. Evidence for dominant particle-core coupling is deduced from these results along with information on excitation energies and electromagnetic transition matrix elements. Implications of the existence of weakly coupled states built on highly excited core states in competition with 1hω single particle (hole) excitations at comparable energies are discussed.