Quadrupole moments of collective structures up to spin ∼65ℏ in 157Er and 158Er: A challenge for understanding triaxiality in nuclei

The transition quadrupole moments, Qt, of four weakly populated collective bands up to spin ∼65ℏ in 157,158Er have been measured to be ∼11eb demonstrating that these sequences are associated with large deformations. However, the data are inconsistent with calculated values from cranked Nilsson-Strutinsky calculations that predict the lowest energy triaxial shape to be associated with rotation about the short principal axis. The data appear to favor either a stable triaxial shape rotating about the intermediate axis or, alternatively, a triaxial shape with larger deformation rotating about the short axis. These new results challenge the present understanding of triaxiality in nuclei.