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The exact nature of the lowest Kμ = 2+ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the y degree of freedom perpendicular to the nuclear symmetry axis. Very few such γ bands have been traced past the usual backbending rotational alignments of high- j nucléons. We have investigated the structure of positive-parity bands in the N = 90 nucleus 156Dy, using the 148Nd(12C,4n) 156Dy reaction at 65 MeV, observing the resulting y-ray transitions with the Gammasphere array. The even- and odd-spin members of the Kμ = 2+γ band are observed up to 32+ and 31+, respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible γ vibration built on the aligned yrast S band are observed up to spins 28+ and 27+. An even-spin positive-parity band, observed up to spin 24+, is a candidate for an aligned S band built on the seniority-zero configuration of the 0+2 state at 676 keV. The crossing of this band with the 0+2 band is at ħωc = 0.28(1) MeV and is consistent with the configuration of the 0+2 band not producing any blocking of the monopole pairing. [ABSTRACT FROM AUTHOR]

The high-spin states of the two neutron-rich nuclei 88Kr52 and 89Rb52 have been studied from the 18O+208Pb fusion-fission reaction. Their level schemes were built from triple β-ray coincidence data, and β-β angular correlations were analyzed in order to assign spin and parity values to most of the observed states. The two level schemes evolve from collective structures to single-particle excitations as a function of the excitation energy. Comparison with results of shell-model calculations gives the specific proton and neutron configurations which are involved to generate the angular momentum alongthe yrast lines. [ABSTRACT FROM AUTHOR]

Odd-odd 136Cs nuclei have been produced in the 18O + 208Pb and 12C + 238U fusion-fission reactions and their γ rays studied with the Euroball array. The high-spin level scheme was built up to ~4.7 MeV excitation energy and spin I ~ 16h from the triple γ-ray coincidence data. The configurations of the three structures observed above ~2 MeV excitation energy are first discussed bγ analogy with the proton excitations identified in the semimagic 137Cs82 nucleus, which involve the three high-j orbits lying above the Z = 50 gap, πg7/2, πd5/2, and πhn1/2- This is confirmed by the results of shell-model calculations performed in this work. [ABSTRACT FROM AUTHOR]

Five N = 82 isotones have been produced in two fusion-fission reactions and their &ggr; rays studied with the Euroball array. The high-spin states of 139La have been identified, while the high-spin yrast and near-to-yrast structures of the four others have been greatly extended. From angular correlation analysis, spin values have been assigned to some states of 136Xe and 137Cs. Several cascades involving &ggr; rays of 139La have been found to be delayed; they deexcite an isomeric state with T1/2 = 315(35) ns located at 1800 keV excitation energy. The excited states of these five N = 82 isotones are expected to be due to various proton excitations involving the three high-j subshells located above the Z = 50 shell closure. This is confirmed by the results of shell-model calculations performed in this work. In addition, high-spin states corresponding to the excitation of the neutron core have been unambiguously identified in 136Xe, 137Cs, and 138Ba. [ABSTRACT FROM AUTHOR]

The 119_126Sn nuclei have been produced as fission fragments in two reactions induced by heavy ions: 12C + 238U at a bombarding energy of 90 MeV and 18O + 208Pb at 85 MeV. Their level schemes have been built from γ rays detected using the Euroball array. High-spin states located above the long-lived isomeric states of the evenand odd-A 120-126Sn nuclei have been identified. Moreover, isomeric states lying around 4.5 MeV have been established in 120,122,124,126Sn from delayed coincidences between the fission fragment detector SAPhIR and the Euroball array. The states located above 3 MeV excitation energy are ascribed to several broken pairs of neutrons occupying the vh11/2 orbit. The maximum value of angular momentum available in such a high-j shell, i.e., for midoccupation and the breaking of the three neutron pairs, has been identified. This process is observed for the first time in spherical nuclei. [ABSTRACT FROM AUTHOR]

The 83, 81As nuclei have been produced as fission fragments in the fusion reaction 18O + 208Pb at 85 MeV bombarding energy and studied with the Euroball array. Medium-spin states of 83, 81As have been established up to ~3.5 MeV excitation energy. From angular correlation analysis, spin values have been assigned to most of the 81As excited states. The behaviors of the yrast structures identified in this work are discussed in comparison with the general features known in the mass région. Then they are compared to the results of two theoretical approaches: the "rotor + quasiparticle" for 81As and the shell model using the effective interactions JUN45 for 83, 81Ks. [ABSTRACT FROM AUTHOR]