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

Photon scattering experiments on the deformed even-even nuclei 164,166,168,170Er provided detailed information on the excitation energies, spins, transition probabilities, and K quantum numbers of low-lying dipole excitations. In the case of 168Er, 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 M1 excitations are compared with the systematics of low-lying orbital M1 strength (open-quote open-quote scissors mode close-quote close-quote) in the neighboring rare-earth nuclei. The observed enhanced E1 transitions are discussed in terms of collective excitations (K=0 octupole bandheads or candidates for 2+circle-times 3- two-phonon excitations) and in the framework of recent microscopic quasiparticle phonon model calculations. copyright 1996 The American Physical Society