Detailed spectroscopy of quadrupole and octupole states in 168 Yb

The low-lying positive-and negative-parity states in Yb-168 have been investigated by means of the (alpha, 2n gamma) fusion evaporation reaction. Using the coincidence method, the level scheme was corrected and extended up to 3MeV, for both the positive-and negative-parity states. Using the new branching ratios determined in the present experiment, the K quantum number was proposed for two negative-parity bands by direct comparison with the Alaga rule. Like in some other nuclei, one negative-parity band was established, decaying predominantly to the gamma-vibrational band. In a second experiment, the lifetimes of the low-lying excited states up to J(pi) = 6(+) in the ground-state band were measured by using the in-beam fast-timing method with the Bucharest mixed high-purity germanium (HPGe) and LaBr3:Ce detector array using the triple-gamma coincidence method. Reduced E2 transition probabilities were extracted from the measured lifetimes and compared with the corresponding observables in neighboring isotopes, showing a smooth behavior with increasing mass. The positive-and negative-parity states as well as E1 and E2 transition probability ratios revealed by these experiments are compared with the interacting boson model in the sd and spdf boson space, and with the confined beta-soft rotor model, and are found to be in good agreement.