Loss of collectivity in the transitional Er156 nucleus at high spin

Abstract

The Cd114(Ca48,6nγ) reaction at 215 MeV has been investigated using the Gammasphere spectrometer to study the high-spin structure of the nucleus 68156Er88. Many new transitions have been established along with definitive spin-parity level assignments from a high-fold angular-distribution analysis. In addition, absolute B(M1) and B(E1) strengths have been inferred from measured γ-ray branching ratios. Strong B(E1) strength (10-3 W.u.) is discussed in terms of possible octupole collectivity at low spin. At high spin, this nucleus undergoes a Coriolis-induced shape transition from a prolate state of collective rotation to a noncollective, triaxial-oblate configuration. The yrast positive-parity structure ultimately terminates in an energetically favored oblate state at Iπ=42+. Several weak high-energy γ-ray transitions have been discovered that feed this favored state. State-of-the-art cranked Nilsson-Strutinsky calculations are used to interpret the high-spin behavior of Er156 and comparisons are made with other N=88 isotones. © 2009 The American Physical Society.