Transition quadrupole moments of high-spin states in 162,163Yb

Abstract Lifetimes of states in 162,163 Yb have been measured by the Doppler-shift recoil-distance method using the reaction 116 Cd ( 50 Ti , x n ) 166−x Yb at 215 MeV . The data were collected in coincidence with a total-energy filter to provide some discrimination on reaction channel. The experimental transition quadrupole moments, Q t , do not agree in detail with predictions from cranked Hartree-Fock-Bogoliubov (HFB) calculations for the yrast band of 162 Yb. In particular, the loss of collectivity occurs at much lower angular momentum than predicted by the calculations. These discrepancies are not understood in state of the art calculations of the nuclear shape. The interaction strength V between the g- and the s-band extracted from the data is very small (| V | ≲ 1 keV). The E1/E2 branching ratios and E1 transition probabilities for decay of states at low spins in the (−, 1) band are large ( B (E1) = 10 −3 B (E1) sp ). The origin of these effects suggests that the (−, 1) band at low frequencies in 162 Yb is predominately an octupole band. Although no stable octupole deformation has been predicted in this mass region, the experimental evidence points to some octupole instability for 162 Yb.