Investigation of γ-vibration and other sidebands in 162164166Er and 154Gd using the (α,2nγ) reaction

Levels in 162164166 Er and 154Gd were studied using the (α,2nγ) reaction at an energy of 24 MeV. Singles spectr, γ-γ coincidence spectra, and angula distributions were obtained using Ge(Li) detectors. Directional correlation measurements were also performed on selected transitions from the isomeric and groundstate decays of 154Tb. Transitions from levels in the γ-vibrational bands up to the 8+' in 162164Er and the 10+' in 166Er were observed and M1/E2 mixtures were determined for many of these transitions. There is a relative shifting upward of the even-spin levels in the γ-band of 166Er while the analogous levels of 162164Er are shifted downward with the effect being most pronounced for 162Er. The standard phenomenological band-mixing parameters z2, z0, and z02 were obtained from γ-ray branching ratio data and the values are probably correlated with the staggering of levels in theγ-bands. The ratios of the intraband E2 transition strengths which are related to the intrinsic quadrupole moments of the ground-state and γ-bands are discussed. A number of other levels are observed in 162164Er and some of these correspond to negative parity states reported in decay studies. Transitions from levels up to 7+ in the γ-vibrational band, 8+ in the K/sup π/ = 4+ band, possibly 11 in the K/sup π/ = 0- band, and 9- in the K/sup π/ = 7- band of 154Gd were observed and M1/E2 mixtures were determined for many of these transitions. There is very little relative shifting of the even or odd levels in the K/sup π/ = 4+ band while for the γ-band the even spin levels are shifted downward. The phenomenological band-mixing parameters z2 and z0 were obtained from the γ-ray branching ratio data. Several other levels are observed in 154Gd, some of which correspond to states reported in decay and particle transfer reaction studies