G. Rainovski

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

A breakthrough was recently obtained in the analysis of the so-called Hyper-Long-HyperDeformed (HLHD) experiment made at the EUROBALL-IV γ-detector array (EB). The 64Ni + 64Ni ⇒ 128Ba* fusion reaction was studied at Ebeam = 255 and 261 MeV, reaching the highest angular momentum that the compound nuclei can accommodate. To date no discrete HD rotational bands have been identified. However, rotational patterns in the form of ridge-structures in three-dimensional (3D) rotational mapped spectra are identified with dynamic moments of inertia J(2) ranging from 71 to 1112 MeV-1 in 12 different nuclei selected by charged particle- and/or γ-gating. The four nuclei, 118Te, 124Cs, 125Cs and 124Xe found with moment of inertia J(2)≥100 2 MeV-1, are most likely hyperdeformed, the remaining nuclei with smaller values of J(2), are considered to be superdeformed, in qualitative agreement with recent theoretical calculations.

Hyperdeformed Shapes and Jacobi Transitions in 126Ba

Systematic searches for exotic shapes, hyperdeformation (HD) and Jacobi transitions, have been made in Hf, Nd, Ba, Xe, Sn and Cd nuclei during the last 4 years, guided by theoretical predictions. The most promising results showing patterns of rotational correlations (e.g. 2. order ridges of multiple rotational bands) are found for 126Xe and 126Ba when the very highest multiplicity cascades are selected by various techniques. In particular, the results on 126Ba obtained in 3 different experiments, using both Gammasphere in Berkeley and Euroball IV in Strasbourg are discussed and compared to theoretical predictions and to simulations by a double‐potential statistical model for population and γ‐decay. A very surprising result was obtained in the last experiment at Euroball, in a full month running time, namely that the observed ridge structure depends very sensitively on the bombarding energy, which points to entrance channel effects. The analysis shows that a discrete HD yrast band intensity will be signifi...

The highest spin discrete levels in 131,132Ce

The three superdeformed (SD) bands in 132Ce and the two SD bands in 131Ce have been extended to higher spin following experiments with the EUROBALL IV spectrometer. The two SD bands in 131Ce have been linked together. However, despite the relatively high population intensity of the bands (up to 5% of the respective channel), it has not been possible to unambiguously link any of the five SD bands into the low-spin, normally deformed structures of 131, 132Ce.

High-spin structure of Ru102

High-spin states in the nucleus 102Ru have been investigated via the 96Zr(13}C,alpha3n) reaction at beam energies of 51 and 58 MeV, using the EUROBALL IV gamma-ray spectrometer and the DIAMANT charged particle array. Several new high-spin bands have been established. The ground state band has been extended up to E_x sim 12 MeV with Ipi = (26+), while the previously published negative-parity bands have been extended up to E_x sim 11 and sim 9 MeV with I pi = (23-) and (20-), respectively. The deduced high-spin structure has been compared with Woods-Saxon TRS calculations and, on the basis of the measured Routhians, aligned angular momenta, and B(M1)/B(E2) ratios, nu h_11/2(g_{7/2},d_{5/2} configurations are suggested for the negative-parity structures.

High-spin structure ofRu102

High-spin states in the nucleus 102Ru have been investigated via the 96Zr(13}C,alpha3n) reaction at beam energies of 51 and 58 MeV, using the EUROBALL IV gamma-ray spectrometer and the DIAMANT charged particle array. Several new high-spin bands have been established. The ground state band has been extended up to E_x sim 12 MeV with Ipi = (26+), while the previously published negative-parity bands have been extended up to E_x sim 11 and sim 9 MeV with I pi = (23-) and (20-), respectively. The deduced high-spin structure has been compared with Woods-Saxon TRS calculations and, on the basis of the measured Routhians, aligned angular momenta, and B(M1)/B(E2) ratios, nu h_11/2(g_{7/2},d_{5/2} configurations are suggested for the negative-parity structures.

Octupole signatures in Ba-124,Ba-125

The γ decay of the nuclei 124,125 Ba has been investigated with the EUROBALL array, using the reaction 64 Ni+ 64 Ni at Ebeam = 255 and 261 MeV. Six new E1 transitions have been found in the nucleus 125 Ba, suggesting a significant role of octupole correlations in the origin of its parity doublets. The J π = 3 − level

Octupole signatures in124,125Ba

The γ decay of the nuclei 124,125 Ba has been investigated with the EUROBALL array, using the reaction 64 Ni+ 64 Ni at Ebeam = 255 and 261 MeV. Six new E1 transitions have been found in the nucleus 125 Ba, suggesting a significant role of octupole correlations in the origin of its parity doublets. The J π = 3 − level

High-spin structure of 102Ru

High‐spin states in the nucleus 102Ru have been studied through the 96Zr(13C,α3n) reaction using the EUROBALL IV γ‐ray spectrometer accompanied by the DIAMANT array for the detection of charged particles. All previously known bands have been extended to higher spins and additional bands have been found. Comparing the experimental Routhians and aligned angular momenta to the predictions of Woods‐Saxon TRS calculations, vh11/2(d5/2,g7/2) configurations have been assigned to the observed negative‐parity bands.

Composite chiral bands in the A∼105 mass region

Composite chiral bands, corresponding to the πg9/2v(h11/2)2 quasiparticle configuration, have been observed in 103Rh and 105Rh. The behaviour of these bands is compared with that of the chiral bands with a πg9/2vh11/2 quasiparticle configuration observed in the odd‐odd 102Rh and 104Rh nuclei. This comparison shows in a model independent way that the energy separation pattern of the chiral partner bands depends strongly on the properties of the triaxial core whilst the dependence on the valence quasiparticle coupling and on the Fermi level is weaker.

Deformation of the very neutron‐deficient rare‐earth nuclei produced with the SPIRAL 76Kr radioactive beam and studied with EXOGAM + DIAMANT

The structure of the very neutron‐deficient rare‐earth nuclei has been investigated in the first experiment with the EXOGAM gamma array coupled to the DIAMANT light charged particle detector using radioactive beam of 76Kr delivered by the SPIRAL facility. Very neutron‐deficient Pr, Nd and Pm isotopes have been populated at rather high spin by the reaction 76Kr + 58Ni at a beam energy of 328 MeV. We report here the first results of this experiment.