K. Zuber

Excited bands in the doubly-magic superdeformed 152Dy nucleus: evidence for the first N = 7 proton hyper-intruder orbital

Abstract Five excited superdeformed bands have been observed in the doubly closed-shell superdeformed nucleus 152 Dy. Three of the new bands are interpreted in terms of single neutron excitations across the N = 86 shell gap. One of these bands appears to partly decay into the yrast superdeformed band. Another band involves a single proton excitation across the Z = 66 shell gap into the N = 7 hyper-intruder orbital. This is the first evidence of the influence of this deformation driving orbital on superdeformed structures in any mass region.

Evidence for the Jacobi shape transition in hot46Ti

The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an experiment using a setup consisting of the combined EUROBALL IV, HECTOR and EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the predictions of the thermal shape fluctuation model shows evidence for the Jacobi shape transition in hot 46Ti. In addition to the previously found broad structure in the GDR lineshape region at 18-27 MeV caused by large deformations, the presence of a low energy component (around 10 MeV), due to the Coriolis splitting in prolate well deformed shape, has been identified for the first time.

Multi-particle excitations in the superdeformed 149Gd nucleus

Abstract Six rotational bands built on superdeformed intrinsic configurations have been observed in the 149 Gd nucleus with the Eurogam spectrometer. Orbital configuration assignments have been suggested on the basis of their effective alignments calculated with the Nilsson-Strutinsky cranking model. Most of the excited bands have identical partners in neighboring nuclei including one case differing by four mass units. Measurements of feeding patterns indicate that the 149 Gd yrast superdeformed band is fed over a wider range of angular momentum than other yrast superdeformed bands in this mass region whereas weaker excited bands in the same nucleus are populated in narrower spin windows.

Prolate and oblate 10+ isomers in 140Sm78 and 142Gd78

Abstract The N = 78 isotones 140Sm and 142Gd have been studied with α-particle- and HI-induced reactions. In both nuclei two close-lying 10+ isomers at ∼ 3.2 MeV have been established, and from the feeding E2 cascades they are characterized as the prolate ν h 11 2 −2 and the oblate π h 11 2 2 excitations. A third E2 cascade feeding into the 142Gd 8+ state is interpreted as the continuation of the collective ground state sequence that might assume the properties of a perfect deformed rotor for spins above 10.

Feeding of the superdeformed yrast band in 149Gd

Abstract The feeding pattern of the superdeformed yrast band in 149 Gd has been found to remain essentially the same, using the 124 Sn+ 30 Si reaction at beam energies of 150, 155 and 160 MeV leading to different input angular momenta and excitation energies in the compound nuclear system. This similarity as well as the relative yields of the superdeformed states as a function of beam energy may be understood in terms of the nuclear level density dependence on deformation and the onset of fission. In addition, it has been shown that, at all three beam energies, the selection of high-energy gamma rays does not enhance the yield of the superdeformed yrast states.

Neutron excitations across the N = 86 superdeformed shell gap

Abstract Based on data obtained with the Eurogam spectrometer, a systematic investigation of superdeformed bands built on single neutron excitations across the N = 86 shell gap has been carried out for gadolinium, terbium, and dysprosium isotopes with 85 ≤ N ≤ 87. In each nucleus, pairs of bands corresponding to degenerate signature partners have been observed. The effective alignment is constant and close to zero for many of the bands, in agreement with cranked shell model calculations for the [402]5/2 and [514]9/2 orbitals. Several bands exhibit non-zero alignments, indicating in some cases the influence of pairing correlations even at high spin and in other cases the occupancy of the [521]3/2 orbital.

Probing the Order-to-Chaos Region in Superdeformed {sup 151}Tb and {sup 196}Pb Nuclei with Continuum {gamma} Transitions

The gamma decay associated with the warm rotation of the superdeformed nuclei 151Tb and 196Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the superdeformed well. A Monte Carlo simulation of the gamma decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength for 1-2 MeV gamma rays, which may be related to the evidence for octupole vibrations in both mass regions.

Search for the Jacobi shape transition in light nuclei

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Unfavoured signature partner superdeformed bands associated with proton excitations in 151Tb

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

-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