155Ho and 157Ho have been populated in the reactions 141Pr(18O,4n) and 146Nd(15N, 4n) at 85 and 74 MeV, respectively. In both nuclei bands built on the 7 2- configuration were established to spin values considerably above the first backbend. A signature dependence in the excitation energies as well as in the ratio of M1 to E2 transition rates is observed below, but not above, the backbend in both nuclei. In 157Ho lifetimes were measured with the recoil-distance method. The ΔI = 2; E2 transition probabilities obtained show very little variation with either signature or spin and no irregularity at the backbend. The signature dependence and strong rise in the ratio B(M1)/B(E2) observed at the backbend in 157Ho therefore must be caused by the B(M1) values. A signature dependence in the B(E2, I → I -1)/B(E2, I → I -2) ratios also found in 157Ho below the backbend is mainly the result of signature dependence in the ΔI = 1 ; E2 transition rates. Qualitatively, most of the features observed can be explained by nonaxial deformations, which change from large negative to slightly positive values of γ at the backbend.
ASJC Scopus subject areas
- Nuclear and High Energy Physics