[en] The aim of this work is to get more information about the population mechanism of superdeformed (SD) bands in the A ≅150 mass region. Usually, SD bands were populated in heavy-ion induced fusion reactions and most of them have been seen in xn exit channels. With the new generation of gamma-ray arrays, we are able to see SD structures populated in charged particle channels. Four experiments have been performed at the Vivitron accelerator in Strasbourg using the EUROGAM 2 spectrometer to study these phenomena (especially in α-particle channels). (author)

No abstract available

[en] Structure of eight experimentally known superdeformed bands in the nucleus ¹⁵¹Tb is analyzed using the results of the Hartree-Fock and Woods-Saxon cranking approaches. It is demonstrated that far going detailed similarities between the two approaches exist and predictions related to the structure of rotational bands calculated within the two models are nearly parallel. An interpretation scenario for the structure of the superdeformed bands is presented and predictions related to the exit spins are made. Small but systematic discrepancies between experiment and theory, analyzed in terms of the dynamical moments, J⁽²⁾, are shown to exist. These discrepancies can be parametrized in terms of a scaling factor f, such that modifications J^(1),(2)→fJ^(1),(2) together with the implied scaling of the frequencies ω→f^-1ω, correspond systematically better with the experimental data (f≅0.9) for both the Woods-Saxon and Hartree-Fock with Skyrme SkM* interactions. The pairing correlations taken into account by using the particle-number-projection technique are shown to increase the disagreement. Sources of these systematic discrepancies are discussed -- they are most likely related to the not yet optimal parametrization of the nuclear interactions used

[en] The EUROGAM Phase I device is almost running for experiments and new technical developments are in progress for its second phase. For example, a composite Ge detector should enable: a very large photopeak efficiency with good energy and timing resolutions; and, the covering, with Ge, of a large portion of 4π-Str. The Clover detector, proposed by the CRN, Strasbourg, is one of this new generation of Ge detectors. It is currently developed in France by the EUROGAM collaboration. The design, the technical characteristics of the counter and the first results of the prototype tests are discussed in this contribution. (author). 1 ref., 2 tabs., 2 refs

[en] Structure of eight superdeformed bands in the nucleus ¹⁵¹Tb is analyzed using the results of the Hartree-Fock and Woods-Saxon cranking approaches. It is demonstrated that far going similarities between the two approaches exit and predictions related to the structure of rotational bands calculated within the two models are nearly parallel. An interpretation scenario for the structure of the superdeformed bands is presented and predictions related to the exit spins are made. Small but systematic discrepancies between experiment and theory, analyzed in terms of the dynamical moments, J⁽²⁾, are shown to exist. The pairing correlations taken into account by using the particle-number-projection technique are shown to increase the disagreement. Sources of these systematic discrepancies are discussed - they are most likely related to the yet not optimal parametrization of the nuclear interactions used. (authors)

[en] Short communication. 3 refs, 1 fig., 1 tab

[en] Linking transitions between the superdeformed (SD) and the normal deformed (ND) wells have been searched in 151Tb nucleus. Two experiments of 5 and 17 days have been performed with EUROBALL IV. Transitions of 2818 keV and 3748 keV with intensities of about 1 % relative to the yrast SD band have been observed. Their decay-out properties are discussed in the text. In addition the eight known SD bands have been extended towards higher rotational frequencies where orbital crossings are observed. For the first time, weakly populated collective ND structures, likely triaxial, similar to the ones recently identified in 152Dy, 153Ho and 155Er nuclei have been observed in 151Tb. The SD and ND structures are interpreted in the frame of Woods-Saxon theoretical calculations

[en] The experimental study of the unresolved rotational bands, forming ridge structures in γ-γ spectra, has been performed on the superdeformed nucleus ¹⁵¹Tb. γ transitions from the reaction ²⁷Al, at 155 MeV, on ¹³⁰Te were measured with EUROBALL IV in high fold coincidence. The analysis of the intensities and count fluctuations of the ridge structures shows the existence of ≅30 discrete rotational bands of superdeformed nature, half of which is in direct coincidence with the superdeformed yrast band. A comparison with band mixing model predictions and with a previous work on the superdeformed nucleus ¹⁴³Eu is presented

[en] Two experiments to identify hyperdeformation in Xe-nuclei have been made using the reaction 82Se(48Ca,xn)130-xXe, the first one with the EUROBALL-IV array equipped with a BGO calorimeter and the second one with the Gammasphere array. A bombarding energy of 195 MeV was used with the VIVITRON and 206 MeV with the ATLAS accelerator. No discrete hyperdeformed bands have been identified, but a ridge structure with 4 (ℎ/2π)²/J ∼ 0.048 MeV corresponding to a very large deformation was observed. A fluctuation analysis revealed that these ridges are composed of more than 10 rotational bands with ≥ 5 transitions each. Seven and four discrete bands extending from I ∼ 20 to I ∼ 60 have been identified in 125Xe and in 126Xe respectively, with a ΔEγ of 100 - 120 keV. These bands are most probably related to a potential energy minimum at ε ∼ 0.35 and a small γ-deformation predicted by Ultimate Crancker calculations. The transition quadrupole moments, crossing frequencies and alignments observed in the bands compare very well with those expected for this minimum

[en] An enhanced population of the ¹⁴⁹Gd yrast superdeformed band has been observed in the reaction ¹²⁴Sn(³¹P,p5n) using the EUROBALL IV multidetector associated with an inner ball. This effect is explained as the consequence of a higher probability of trapping residual nuclei into the superdeformed well whose depth has been increased due to favorable temperature and of total energy and angular momentum selection with the inner ball