Systematics of low-lying dipole excitations in the deformed even-even nuclei Er-164,Er-166,Er-168,Er-170

Photon scattering experiments on the deformed even-even nuclei {sup 164,166,168,170}Er provided detailed information on the excitation energies, spins, transition probabilities, and {ital K} quantum numbers of low-lying dipole excitations. In the case of {sup 168}Er, in addition, parities of the excited states were determined model independently by measuring the linear polarization of the scattered photons using a sectored Ge-Compton polarimeter with a BGO{endash}anti-Compton shield. The results for {ital M}1 excitations are compared with the systematics of low-lying orbital {ital M}1 strength ({open_quote}{open_quote}scissors mode{close_quote}{close_quote}) in the neighboring rare-earth nuclei. The observed enhanced {ital E}1 transitions are discussed in terms of collective excitations ({ital K}=0 octupole bandheads or candidates for 2{sup +}{circle_times}3{sup {minus}} two-phonon excitations) and in the framework of recent microscopic quasiparticle phonon model calculations. {copyright} {ital 1996 The American Physical Society.}