CONFIGURATION-DEPENDENT TRANSITION RATES IN HO-157

The lifetimes of the high-spin states of 157Ho have been measured using the Doppler shift attenuation method (DSAM). The comparison of the observed shifts following the 124Sn(37Cl, 4n) reaction at a beam energy of 150 MeV, and the 142Ce(19F, 4n) reaction at 85.5 MeV shows that the yrast states above spin 71 2- are much less collective than the states below. Transition quadrupole moments were obtained for states from spin 45 2- to 55 2- h {combining short stroke overlay} in the yrast band, and from 37 2- to 53 2- h {combining short stroke overlay} in the third lowest negative-parity band. The difference in collectivity agrees with the assignment of these bands to a [523] 7 2-(h 11 2) and a [541] 1 2-(h 9 2) quasiproton excitation, respectively. However, it cannot explain the difference in the i 13 2 neutron crossing frequencies of the two bands. The measured Qt values for the [523] 7 2- configuration are compared to those of other N = 90 isotones. © 1990.