Wobbling phonon excitations, coexisting with normal deformed structures in 163Lu

Wobbling is a rotational mode unique to a triaxial body. The Lu-Hf isotopes with N similar to 94 at high spin provide a possible region of nuclei with pronounced triaxiality. We have investigated Lu-163 through the fusion-evaporation reaction La-139(Si-29,5n)Lu-163 with a beam energy of 152 MeV. Three excited bands decaying into the known, presumably triaxial, superdeformed (TSD) band built on the i(13/2) proton orbital are observed. The electromagnetic properties of the connecting transitions from the two strongest populated excited TSD bands have been investigated. New particle-rotor calculations in which one i(13/2) quasiproton is coupled to the core of triaxial shape produce a variety of bands, whose properties can clearly be interpreted either as wobbling or cranking motion of the core. Evidence for the assignment of the excited TSD bands as one, and possibly even two wobbling phonon modes built on the yrast TSD band in Lu-163 is given. These triaxial bands coexist with bands built on quasiparticle excitations in the normal deformed (ND) minimum for which new data are also presented. (C) 2001 Elsevier Science B.V. All rights reserved.