Hartree-Fock-Bogoliubov Calculations of the Rotational Band of the Very Heavy 254^{254}No Nucleus

We report on Hartree-Fock-Bogoliubov (HFB) calculations of the ground-state rotationnal band of the heavy nucleus $^{254}$No recently observed experimentally. The calculated quadrupole deformation is consistent with the experimental value of $\beta=0.27$ and is almost constant over the whole band. We also reproduce fairly well the excitation spectra and moments of inertia of this isotope up to the maximal experimentally observed state of spin 20. The rather high stability of this nucleus against fission is illustrated by the deformation energy curve providing very high fission barriers at zero spin within the HFB and HFB plus Lipkin-Nogami formalisms. The variation of these barriers with increased angular velocities is also studied.Comment: 4 pages (LaTeX), submitted to Eur. Phys. J A, dedicated to the memory of J. Piperov

A simple model for the quenching of pairing correlations effects in rigidly deformed rotational bands

Using Chandrasekhar's S-type coupling between rotational and intrinsic vortical modes one may simply reproduce the HFB dynamical properties of rotating nuclei within Routhian HF calculations free of pairing correlations yet constrained on the relevant so-called Kelvin circulation operator. From the analogy between magnetic and rotating systems, one derives a model for the quenching of pairing correlations with rotation, introducing a critical angular velocity -- analogous to the critical field in supraconductors -- above which pairing vanishes. Taking stock of this usual model, it is then shown that the characteristic behavior of the vortical mode angular velocity as a function of the global rotation angular velocity can be modelised by a simple two parameter formula, both parameters being completely determined from properties of the band-head (zero-spin) HFB solution. From calculation in five nuclei, the validity of this modelised Routhian approach is assessed. It is clearly shown to be very good in cases where the evolution of rotational properties is only governed by the coupling between the global rotation and the pairing-induced intrinsic vortical currents. It therefore provides a sound ground base for evaluating the importance of coupling of rotation with other modes (shape distortions, quasiparticle degrees of freedom).Comment: 10 pages, 8 figures. Submited to PR

On the equivalence of pairing correlations and intrinsic vortical currents in rotating nuclei

The present paper establishes a link between pairing correlations in rotating nuclei and collective vortical modes in the intrinsic frame. We show that the latter can be embodied by a simple S-type coupling a la Chandrasekhar between rotational and intrinsic vortical collective modes. This results from a comparison between the solutions of microscopic calculations within the HFB and the HF Routhian formalisms. The HF Routhian solutions are constrained to have the same Kelvin circulation expectation value as the HFB ones. It is shown in several mass regions, pairing regimes, and for various spin values that this procedure yields moments of inertia, angular velocities, and current distributions which are very similar within both formalisms. We finally present perspectives for further studies.Comment: 8 pages, 4 figures, submitted to Phys. Rev.

Skyrme mean-field study of rotational bands in transfermium isotopes

Self-consistent mean field calculations with the SLy4 interaction and a density-dependent pairing force are presented for nuclei in the Nobelium mass region. Predicted quasi-particle spectra are compared with experiment for the heaviest known odd N and odd Z nuclei. Spectra and rotational bands are presented for nuclei around No252,4 for which experiments are either planned or already running.Comment: 13 pages LATEX, elsart style, 6 embedded eps figure

Higher Tamm-Dankoff Approximation for rotational states

Within the Higher Tamm Danco® Approximation (HTDA), single particle states associated with a mean ¯eld of the Hartree-Fock type are used into shell model like calculations. Recently, this approach has been used for ground state calculations in magic nuclei and in the N = Z mass region, as well as to study properties of some important isomeric states. The Cranking version of this formalism (Cr. HTDA) represents an attempt to reproduce rotational bands up to high spins in heavy nuclei. In this context, through the use of the mean ¯eld part of HTDA, many deformation and rotation e®ects (as intruder orbitals and e®ects of the time reversal symmetry breaking) are included in the con¯guration space. This work discusses the Cr. HTDA results obtained for two Pb isotopes (in order to test the approach), when using up to 2 particles - 2 holes excitations and provides tests for enlargement of the con¯guration space by 4 particle - 4 holes excitations. It is focused on the con¯guration space properties, improvement of truncation schemes, computational problems and saturation behavior of some physical quantities