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[en] Transition energies, incremental alignments of angular momentum, dynamic moments of inertia of triaxial superdeformed bands in rare-earth nuclei have been examined systematically. It is found that the incremental alignments are nearly constant and their dynamic moments of inertia are quite similar. Therefore these triaxial superdeformed bands in rear-earth nuclei are identical bands
[en] The phenomenon of identical bands is studied by analyzing the distributions of fractional changes in the dynamical moments of inertia of pairs of bands in superdeformed (SD) nuclei. These distributions are found to exhibit a peak with a centroid at nearly zero. Their widths increase in going from the SD bands in the mass A ∼ 150, to the SD bands in the mass ∼190 and to the normally-deformed bands in the rare-earth region. These differences may be attributed to the weaker pairing correlations and the stabilizing role of intruder orbitals on the structures of SD bands. Precise level lifetimes have been measured for various pairs of identical SD bands in Gd and Dy isotopes. By comparing the derived quadrupole moments with calculations performed in the framework of the cranking Skyrme-Hartree-Fock model, it is shown that, independently of the intrinsic configuration and of the proton and neutron numbers, the charge moments calculated with respect to the doubly-magic SD core of 152Dy can be expressed in terms of independent contributions from the individual hole and particle orbitals. (author)
[en] Although four decades ago it had been conclusively shown that the first excited 02+ state in 15666Dy90 was a pairing isomer, the lessons of this identification has taken a long time to connect with the Nuclear Structure Community. The 02+ states that can be populated significantly with two particle neutron transfer, all have large enough cross-sections to demonstrate that simple monopole pairing in theoretical descriptions will be insufficient. The conclusion that these states cannot be associated with time-dependent β vibrations of the nuclear shape is also supported by their very weak excitation in inelastic scattering processes such as (d,d'). Blocking of the coupling of the single particle neutrons in odd nuclei to the 02+ states near N=90 have shown that a major part of their configurations is a pair of neutrons in the 11/2- Nilsson orbit. This high-K orbit is extruded from the h11/2 shell to the Fermi surface by the increasing deformation caused by adding neutrons outside the N=82 core. These data confirm the separation of prolate-prolate and oblate-oblate pairing. At iThemba LABS we have used conventional γ-ray spectroscopy to investigate structures in the pairing gaps of even-even nuclei in the ranges Z=62-70 and N=88-92, in particular to study the systematics of the excited Kπ = 02+2 and 2γ+ positive parity bands. We find that the 02+ bands all have moments-of-inertia that are greater than those of the ground state 01+1 bands, in complete contradiction to the predictions of all Interacting Boson Models (IBM). The larger moments-of-inertia for 02+ bands are consistent with reduced pairing due to the low density of oblate (high-W) orbitals near the Fermi surface. The odd spin members of the γ bands all track the ground state bands while the even spin members can mix with the 01+ and 02+ bands. Indeed the γ bands and 02+ bands cross and interact strongly affecting the signature splittings S(I) observed in the γ bands. The systematic data will be discussed in terms of the Triaxial Projected Shell Model (TPSM) and the 5-Dimensional Collective Model (5-DCM). This document is composed of an abstract and the slides of the presentation. (author)
[en] Level densities and radiative strength functions in 171Yb and 170Yb nuclei have been measured with the 171Yb(3He,3He(prime) γ)171Yb and 171Yb(3He, αγ)170Yb reactions. A simultaneous determination of the nuclear level density and the radiative strength function was made. The present data adds to and is consistent with previous results for several other rare earth nuclei. The method will be briefly reviewed and the result from the analysis will be presented. The radiative strength function for 171Yb is compared to previously published work.
[en] The sequence of nuclear shapes from spherical to prolate or oblate to octupole involves a corresponding sequence of symmetry breakings. Each successive symmetry breaking leads to a more complex nuclear spectroscopy which displays the distinguishing features of that nuclear shape. The author discusses the particular spectroscopic features which signal the existence of octupole deformation (reflection asymmetry) and apply them to a number of odd-A and odd-odd nuclei in the actinide and rare earth regions