Triaxiality in 166Er

Abstract

The nucleus 166Er has been Coulomb excited using beams of 16O, 32S and 58Ni. An almost complete set of reduced E2 matrix elements for the ground- and γ-bands up to spin 14 + and 12 +, respectively, has been measured. A total of 44 E2 matrix elements have been determined in a model-independent way, including the static quadrupole moments up to spin 10 + of the ground band and spin 8 + of the γ-band. The data are compared with the predictions of geometric collective models and with the IBA-1 model. Overall, the experimental data are well reproduced by both the asymmetric rotor model and the rotation-vibration model. The data slightly favours the latter model and suggest that the collective structure of 166Er can be understood in terms of a varying dynamic triaxiality from γ ≈ 18° for the ground state to γ ≈ 10° for the higher spin states of the ground band and for the γ-band. The data also suggest that the Coriolis interaction is strong already at spin 8 + in both the ground band and the γ-band.