Isospectral superdeformed bands in the N = 46 nuclei 88Mo and 89Tc

Superdeformed bands in ⁸⁸Mo and ⁸⁹Tc were populated using ⁴⁰Ca-induced fusion-evaporation reactions on ⁵⁸Ni at a beam energy of 185MeV. Gamma-rays emitted in the reactions were detected using the Gammasphere spectrometer, in coincidence with charged particles detected by the Microball array. A new superdeformed band was assigned to the nucleus ⁸⁸Mo, leading to a revisit of earlier configuration assignments for superdeformed structures in this nucleus. In particular, the theoretical interpretation of a pair of identical (isospectral) superdeformed bands in ⁸⁸Mo/⁸⁹Tc is discussed. The configurations that are assigned to the four SD bands belonging to ⁸⁸Mo have properties that are predicted to be significantly affected by pair correlations.Received: 1 October 2003, Revised: 30 January 2004, Published online: 21 September 2004PACS: 21.10.Re Collective levels - 21.60.Cs Shell model - 23.20.Lv transitions and level energies - 27.50. + e K. Lagergren: Present address: Department of Physics, Florida State University, Tallahassee, FL 32306, USA;A. Görgen: Present address: DAPNIA/SPhN, CEA Saclay, F-91191 Gif-sur-Yvette Cedex, France.     

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.     

New excited superdeformed bands in heavy Pb nuclei: Clue for an octupole softness near the N = 118 gap at large deformation

We report the identification of six new superdeformed (SD) bands in ^197,198Pb observed with the EUROBALL IV spectrometer. The results are interpreted in the framework of cranked Hartree-Fock calculations with approximate projection on the particle number by means of the Lipkin-Nogami method. A mixing between quasi-particle excitations and an octupole vibration is suggested in the two SD isotopes. We have estimated the ordering of the neutron valence orbitals and confirm indirectly a N = 118 SD gap. Received: 20 December 2000 / Accepted: 24 January 2001     

On the fine structure of the rotational bands of superdeformed nuclei

It is shown that the staggering of the energy levels of the superdeformed rotational bands can be explained from first principles, using the standard microscopic Hamiltonian with the pairing, quadrupole, and hexadecapole residual interactions, as resulting from rotation-induced nonadiabatic distortion of the mean field in the nucleus. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 231–236 (25 August 1996)     

Band head spin assignment of superdeformed bands in 86Zr

Two parameter expressions for rotational spectra viz. variable moment of inertia (VMI), ab formula and three parameter Harris ω² expansion are used to assign the band head spins (I₀) of four rotational superdeformed bands in ⁸⁶Zr. The least-squares fitting method is employed to obtain the band head spins of these four bands in the A~80 mass region. Model parameters are extracted by fitting of intraband γ-ray energies, so as to obtain a minimum root-mean-square (rms) deviation between the calculated and the observed transition energies. The calculated transition energies are found to depend sensitively on the assigned spins. Whenever an accurate band head spin is assigned, the calculated transition energies are in agreement with the experimental transition energies. The dynamic moment of inertia is also extracted and its variation with rotational frequency is investigated. Since a better agreement of band head spin with experimental results is found using the VMI model, it is a more powerful tool than the ab formula and Harris ω² expansion.     

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.     

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.     

Yrast bands in N = 91 isotones

The in-beam spectroscopy on N = 91 isotones has been carried out using the ¹²C + ¹⁵⁰Nd reaction. The νi _13/2 and νh _11/2 bands of ¹⁵³Sm have been extended up to 33/2⁺ and 31/2^-, respectively. Two new γ-rays have been located on the top of the unfavored band with νi _13/2 configuration in ¹⁵⁷Dy. Two identical relationships have been established in the low-spin region of the yrast νi _13/2 configuration between ¹⁵³Sm and ¹⁵⁵Gd, and between unfavored bands of ¹⁵⁵Gd and ¹⁵⁷Dy. Here all these nuclei have the same neutron number N = 91. Received: 28 June 2000 / Accepted: 20 October 2000     

Quadrupole moments of superdeformed bands in 193Tl

Lifetimes of states in the two strongest superdeformed (SD) bands in ¹⁹³Tl were measured using the Doppler-shift attenuation method. The reaction ¹⁷⁶Yb(²³Na,6n)¹⁹³Tl at a beam energy of 129 MeV was used and γ-rays were detected by the Gammasphere array. Quadrupole moments of 18.3(10) eb and 17.4(10) eb were extracted for SD bands 1 and 2, respectively, using the fractional Doppler-shifts of the SD transitions. The previously reported linking transitions of these SD bands to normal deformed near yrast levels could not be confirmed. No other candidates for linking transitions could be established. Received: 27 April 1999