O. Möller

Transition probabilities in the X(5) candidate

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.

^{122}

Excited states in the deformed nucleus 168Er have been studied with high energy resolution in the (p, t) reaction, with the Munich Q3D spectrograph. A large number of excited 0+ states (25) and 2+ states (64) have been assigned up to 4.0-MeV excitation energy. This allows detailed investigations along two directions of current interest: first, an extension of microscopic model interpretations into the region of medium level density above the pairing gap; second, a first analysis of the statistical fluctuation (order/chaos) properties of pure sequences of levels, in one deformed nucleus. Predictions of two models (the quasiparticle-phonon model and the projected shell model) are compared to the data, and it is concluded that, in both cases, mixing of more configurations is required in the wave functions.

Ba

Low-lying collectively excited states of 128 Xe were investigated by γ-ray spectroscopy following the 12 C( 128 Xe, 128 Xe*) 12 C projectile Coulomb excitation reaction. Nineteen absolute E2 transition strengths were obtained including the first measurement of the critical B(E2) decays from the second and third J π = 0 + states. These data are compared with the theoretical predictions of the critical point symmetry E(5) and allow us to conclude that 128 Xe is not an E(5) nucleus as previously suggested, leaving 130 Xe as the most likely candidate among the Xe isotopes.

High-resolution study of 0+ and 2+ excitations in 168Er with the (p, t) reaction

The energy spectra and relative transition rates of 176,178,180Os were found to be very similar to the values calculated in the framework of the critical point symmetry X(5). In order to enable more stringent tests, including also absolute transition probabilities, two coincidence RDDS lifetime measurements were performed at the Laboratori Nazionali di Legnaro with the GASP spectrometer using the 152,154Sm(29Si,5n)176,178Os reactions. The deduced transition quadrupole moments in 178Os agree well with the X(5) predictions. For 176Os only preliminary results were obtained so far. These preliminary data support an X(5) like structure also in the case of 176Os. The experimental data of both nuclei are compared to calculations in the framework of the interacting boson model (IBM) and of the general collective model (GCM).

Robust test of E(5) symmetry in 128Xe

Lifetime measurements in 134Pr were performed by means of the Recoil distance Doppler‐shift and Doppler‐shift attenuation methods using the multidetector array EUROBALL, in conjunction with the inner BGO ball. The derived B(E2) transition strengths within the two bands candidates for chiral partners behave differently with increasing spin while the corresponding B(M1) values have a similar behaviour within the experimental uncertainties.

Test of the critical point symmetry X(5) in neutron deficient osmium isotopes at A≈180

Six lifetimes have been determined in the 5/2+ [642] band from vi13/2 parentage in 167Yb by means of Recoil distance Doppler-shift (RDDS) measurements carried out at the Cologne FN tandem. The deduced transition strengths and the level scheme are reasonably described by Particle plus triaxial rotor model (PTRM) calculations except for the behavior of the quadrupole collectivity in the two signatures of the 5/2+[642] band. In that band, the quadrupole collectivity of the favored signature is appreciably larger than this of the unfavored signature. The effect increases with increasing the spin. Naturally, the rigid PTRM cannot explain these features, but the structure of its wave functions suggests a possible solution. It is associated with the enhanced contribution of low-Ω orbitals from vi13/2 parentage in the favored signature compared to the unfavored one. This could selectively increase the deformation of the favored signature band members and give rise to a dynamic shape coexistence taking place between the two signatures which needs quantitative explanation by future theoretical work.

Transition Probabilities And Chiral Symmetry In 134Pr

The one-quadrupole phonon excitation of mixed symmetry, the 2+1,ms state, is a fundamental building block of nuclear structure. This article gives a summary of our recent experimental research on this excitation mode in the A = 90 and A = 130 mass regions.

Different collectivity in the two signatures of the i13/2 stemming band in 167Yb

The one-quadrupole phonon excitation of mixed symmetry, the 2+1,ms state, is a fundamental building block of nuclear structure. This article gives a summary of our recent experimental research on this excitation mode in the A = 90 and A = 130 mass regions.

Exotic ideas on mixed proton-neutron symmetry and their manifestation in heavy nuclei

The transition strenghts for the low—lying levels of 122,124Ba have been determined analysing the Recoil Distance Doppler Shift data by the Differential Decay Curve Method. The trend of normalised B(E2) reveals a drop in correspondance of the 81+ state. This feature is also present in 122Ba: entering the backbending region the interplay between collective and quasiparticle degrees of freedom have to be carefully taken into account.

The beauty of good data: Unveiling the traces of mixed symmetry

Low-lying collectively excited states of 128 Xe were investigated by γ-ray spectroscopy following the 12 C( 128 Xe, 128 Xe*) 12 C projectile Coulomb excitation reaction. Nineteen absolute E2 transition strengths were obtained including the first measurement of the critical B(E2) decays from the second and third J π = 0 + states. These data are compared with the theoretical predictions of the critical point symmetry E(5) and allow us to conclude that 128 Xe is not an E(5) nucleus as previously suggested, leaving 130 Xe as the most likely candidate among the Xe isotopes.