Evidence for triaxial deformation near N=86: Collective bands in 152,153Dy and 153Ho

The N=86,87 isotopes of dysprosium and holmium have been investigated using the Eurogam II γ-ray spectrometer. A new collective rotational band has been observed in 153Ho and the previously observed νi13/2 band in 153Dy has been extended to much higher spin. Comparing these bands and similar bands in 152Dy with the collective bands in the N=90 isotopes of Dy, Ho, and Er suggests that the first h11/2 proton crossing is not observed at N=86,87. This observation has led to the reinterpretation of four of the previously observed bands in 152Dy. It is proposed that the low deformation collective bands in 152,153Dy and 153Ho are associated with a triaxial shape with large positive gamma and that they have a similar origin to the recently observed triaxial superdeformed bands in 163–165Lu.