Identical superdeformed bands

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 massA～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 of¹⁵²Dy can be expressed in terms of independent contributions from the individual hole and particle orbitals.     

Evidences for magicity in superdeformed shapes

Many empirical evidences that point to the existence of preferred magic nucleon numbers for superdeformed (SD) shapes are presented in this paper. We use a simple premise based on the 4-parameter formula fitted using observed γ-rays of SD bands. In particular, plots of γ-ray energy ratios, nuclear softness parameter values and the number of SD bands for given N and Z are used to pinpoint the magicity (N, Z numbers) that are most favoured as the SD magic numbers. This analysis also leads to several new predictions on the occurrence of SD bands specially in neutron-rich nuclei.     

Superfluid-to-normal phase transition in superdeformed bands

A semiclassically exact solution for the second inertial parameter B is found for the superfluid and normal phases. An interpolation between these limiting values shows that B changes sign in the transition region at the spin I _c that is critical for the rotational spectrum. A superfluid-to-normal transition reveals itself in a specific variation of B versus the spin I. Experimental data show the existence of a transition for superdeformed bands in the A～80, 130, and 150 mass regions and for some bands characterized by a normal deformation. A transition to the normal phase explains the extreme regularity of superdeformed bands.     

Excited superdeformed band in146Gd

A non-yrast superdeformed band has been found in¹⁴⁶Gd using the¹¹⁰Pd(⁴⁰Ar, 4n)¹⁴⁶Gd reaction. The nuclear assignment was made from the analysis of an experiment using a backed target. This band and the previously identified yrast SD band are probably not signature partners.     

Lifetimes and lineshapes in superdeformed bands

The effective lifetimes and the intensity of the discrete transitions of the superdeformed band in¹⁵²Dy are described using a statistical model based on a Monte Carlo simulation. The effect of the transition strength in the continuum and the energy dependence of the barrier are investigated. The importance of the mixing of superdeformed and normal states for the resulting feeding times and intensities is emphasized. The calculations are compared to experimental data, and it is shown that the discrete line shapes are sensitive to the transition strength in the continuum.     

Favoured superdeformed states in 89Tc

A superdeformed band consisting of a cascade of ten γ-ray transitions has been identified and assigned to the nucleus ⁸⁹Tc, close to the proton dripline. The quadrupole moment of the band (Q _t= 6.7^+3.0 _−2.3 eb, as measured by the Residual Doppler Shift Method) as well as a large dynamic moment of inertia point to a highly elongated shape. With a relative population of approximately 15% of the γ-ray flux in the ⁸⁹Tc exit channel, the band is among the most intense superdeformed bands observed to date. Received: 6 July 1999     

A superdeformed band in131Ce

A rotational band of 16γ-rays has been found in¹³¹Ce with a high moment of inertia indicating a deformation ε₂～0.38 and extending to spin ～40?. Its intensity is ～～5% of the total in¹³¹Ce, confirming a difference in the intensity systematics for superdeformed states in Ce nuclei compared with Nd.     

Observation of superdeformed states in 88Mo

High-spin states in ⁸⁸Mo were studied using the Gammasphere germanium detector array in conjunction with the Microball CsI(Tl) charged-particle detector system. Three γ-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A= 80 region have been identified and assigned to the nucleus ⁸⁸Mo. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of β₂≈ 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three bands are assigned to two-quasi-particle proton configurations at superdeformed shape. Received: 20 May 1999 / Revised version: 25 August 1999     

First triaxial superdeformed band in 170Hf

First evidence is presented for triaxial superdeformation in ¹⁷⁰Hf. High-spin states in this nucleus have been investigated in a γ-ray coincidence measurement using the EUROBALL spectrometer array. A new band was discovered which has moments of inertia that are very similar to the ones of triaxial superdeformed bands in neighbouring Hf and Lu nuclei. The intensities with which these bands are populated are different from what may be expected from calculated potential-energy minima. Received: 11 September 2002 / Accepted: 15 October 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: neusser@iskp.uni-bonn.de Communicated by D. Schwalm     

Observation of superdeformed bands in194Hg

Two rotational bands, with energy spacings characteristic of superdeformed shapes, have been observed following bombardment of¹⁵⁰Nd with⁴⁸Ca. The more intensively populated band consists of 18 transitions and is assigned to¹⁹⁴Hg. The depopulation of this band occurs around spin 10. The second band, consisting of at least 16 transitions, was populated less strongly and is tentatively assigned to¹⁹⁴Hg also. The lowest level in this band is assigned spin 8. The energy differences between transitions for both bands decrease from ～40 keV at low rotational frequencies to ～30 keV at the highest observed frequencies. The moments of inertia of the bands are similar to those of the two previously observed superdeformed bands in^191,192Hg. The similarities and differences of the four known bands in the mercury region are discussed.     

Observation of a superdeformed band in192Pb

A new superdeformed band, identified in data from the²⁴Mg+¹⁷³Yb reaction, is assigned to¹⁹²Pb on the basis of excitation function and coincidence results. Properties of this band are discussed briefly, and compared to the superdeformed bands known in other Pb nuclei.