C. M. Petrache

One- and two-phonon wobbling excitations in triaxial 165Lu

High-spin states in Lu-165 have been investigated by in-beam gamma-ray coincidence spectroscopy using the EUROBALL spectrometer array. Two new excited rotational bands have been discovered with features similar to a previously known triaxial superdeformed band in that nucleus. Comparison of the decay pattern of these bands, in particular the unusually large E2 transition strength from the first excited to the yrast superdeformed band, to theoretical calculations shows that they belong to a family of wobbling excitations with phonon numbers n(w) = 0, 1 and 2. These results, together with evidence for nuclear wobbling in the neighbouring isotopes Lu-163 and Lu-167, firmly establish this mode of excitation in the A = 165 mass region. The observation of wobbling is a unique signature of stable nuclear triaxiality

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. (Less)

Isospin mixing in the N = Z nucleus 64Ge

Abstract The N = Z nucleus 64 Ge has been investigated in two experiments using the EUROBALL III and EUROBALL IV spectrometers coupled to ancillary devices. Multipole mixing ratios, linear polarization and picosecond lifetimes for various transitions have been measured. The linear polarization results determine unambiguously the multipole character of the 5 − →4 + 1665xa0keV transition, allowing to extract the electric dipole strength and to investigate for the first time the amount of isospin mixing implied by the presence of a forbidden E1 transition.

Search for the Jacobi shape transition in light nuclei

Abstract.The

Detailed study of magnetic rotation in 196Pb

gamma

Transition probabilities in the X(5) candidate

-rays following the reaction 105 MeV 18O + 28Si have been measured using the EUROBALL IV, HECTOR and EUCLIDES arrays in order to investigate the predicted Jacobi shape transition. The high-energy

^{122}

gamma

Ba

-ray spectrum from the GDR decay indicates the presence of large deformations in the hot 46Ti nucleus, in agreement with new theoretical calculations based on the rotating liquid-drop model.

Charged particle feeding of hyperdeformed nuclei in the A=118?126 region

Abstract High-spin states in 196 Pbxa0have been populated in two different heavy-ion-induced reactions using thin and Au-backed targets, respectively. Gamma-ray coincidences were measured using the EUROBALL spectrometer array. Five new magnetic-rotational bands have been found. The previously known four bands have been extended and some of their levels have been reordered. With one exception, all the bands have been connected to lower-lying states and excitation energies, spins and parities have been determined. From the systematic properties of the bands and from comparison to tilted-axis cranking calculations, arguments for configuration assignments to the bands are derived. It is suggested that the bands are based on proton 11 − and 8 + particle states coupled to various neutron–hole excitations.

Hyperdeformed Shapes and Jacobi Transitions in 126Ba

To investigate the possible X(5) character of {sup 122}Ba, suggested by the ground-state band energy pattern, the lifetimes of the lowest yrast states of {sup 122}Ba have been measured, via the recoil distance Doppler-shift method. The relevant levels have been populated by using the {sup 108}Cd({sup 16}O,2n){sup 122}Ba and the {sup 112}Sn({sup 13}C,3n){sup 122}Ba reactions. The B(E2) values deduced in the present work are compared to the predictions of the X(5) model and to calculations performed in the framework of the IBA-1 and IBA-2 models.