The quadrupole moments of strongly deformed, ultrahigh-spin bands in the nucleus 154Er have been measured for the first time, providing a calibration for recent measurements made for similar bands in 157Er and 158Er using the same method. High-spin states up to ∼52ħ have been populated using the fusion-evaporation reaction 110Pd(48Ti,4nγ)154Er at a beam energy of 215 MeV, in an experiment performed at the ATLAS facility at Argonne National Laboratory, USA, using the Gammasphere detector array.

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... wo new ultrahigh-spin bands, believed to be triaxially deformed, have been observed in 154Er in addition to the known triaxial strongly deformed (TSD) band and superdeformed (SD) axially symmetric prolate band. The quadrupole moments, Qt, of three of these bands have been measured using the Doppler-shift attenuation method (DSAM), with values of 11.0 ± 0.6 eb for the known TSD band, 19.5 ± 1.5 eb for the SD band and 10.0 ± 0.9 eb for one of the new bands. Cranked Nilsson-Strutinsky (CNS) calculations are compared with results and possible nucleon configurations are discussed. A configuration similar to that of the yrast SD band of the isotone 152Dy is assigned to the 154Er SD band. Based on their Qt, the triaxial bands appear more consistent with configurations corresponding to a TSD shape with a negative γ deformation parameter. The Qt of ∼11 eb is consistent with previous results for the four TSD bands in 157,158Er. These results challenge theoretical calculations that predict positive-γ TSD shapes to be energetically favoured over negative-γ shapes.