Low-energy electric and magnetic dipole excitations in 166Er

Low-energy dipole excitations in 166Er were investigated via nuclear resonance fluorescence using a quasi-monoenergetic, linearly polarized photon beam produced at the High Intensity gamma$ray Source (HIgS) facility at Duke University. The parity of the excited states was determined from the azimuthal asymmetry in the intensities of resonantly scattered gamma rays with respect to the polarization plane of the incident beam. Electric and magnetic dipole strengths were extracted for excitation energies between 2.2 and 3.5 MeV. The results are interpreted in terms of the nuclear scissors mode by comparing with large-scale shell-model calculations based on the Quasiparticle Vacua Shell Model. In addition, the characteristics of the E1 excitations are examined in comparison with those of neighboring rare-earth nuclei to explore their relations to collective octupole-gamma-vibrational two-phonon excitations.