(α, 2nγ) Studies of γ-vibrational and other side-bands in 162, 164, 166Er

Abstract

Levels in 162, 164, 166Er have been studied using the (α, 2nγ) reaction at an energy of 24 MeV. Singles spectra, γ-γ coincidence spectra, and angular distributions were obtained using Ge(Li) detectors. Transitions from levels in the γ-vibrational bands up to the 8 +' in 162, 164Er and 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 162, 164Er are shifted downward with the effect being most pronounced for 162Er. The standard phenomenological band-mixing parameters z 2 and z 02 were obtained from γ-ray branching ratio data and the values are probably correlated with the staggering of levels in the γ-bands. The ratios of the intraband and interband 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 162, 164Er and some of these correspond to negative parity states reported in decay studies.