COLLECTIVE GAMMA-VIBRATIONAL BANDS IN HO-165 AND ER-167

The nuclear structures of Ho-165 and Er-167 have been investigated by means of Coulomb excitation. These nuclei excited at moderate spins ex hibit gamma-vibrational bands with K-pi = 11/2(-), 3/2(-) in Ho-165 an d K-pi = 11/2(+) in Er-167. The gamma-vibrational bands in Ho-165 are found to be isospectral; having very nearly identical in-band beta-ray energies. Gamma-ray branching ratios are analysed to extract informat in on collectivity and Coriolis mixing. Experimental results are compa red with calculations performed with the Cranked Shell Model + RPA + p article-vibration coupling and by invoking the generalized intensity r elations (GIR) in the unified model scheme. Although this model explai ns many features of the data, puzzling aspects such as identical trans ition energies for the bands in Ho-165 remain unexplained. The role of the K quantum number in identical bands is discussed. (C) 1997 Elsevi er Science B.V.