W. Kleinig

Description of the dipole giant resonance in heavy and superheavy nuclei within Skyrme random-phase approximation

W. Kleinig, V.O. Nesterenko, J. Kvasil, P.-G. Reinhard and P. Vesely 1 Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Moscow region, 141980, Russia∗ 2 Technische Universität Dresden, Inst. für Analysis, D-01062, Dresden, Germany 3 Institute of Particle and Nuclear Physics, Charles University, CZ-18000, Praha 8, Czech Republic and 4 Institut für Theoretische Physik II, Universität Erlangen, D-91058, Erlangen, Germany (Dated: May 30, 2008)

TDDFT with Skyrme forces: Effect of time-odd densities on electric giant resonances

Time-odd densities and their effect on electric giant resonances are investigated within the self-consistent separable random-phase-approximation (SRPA) for a variety of Skyrme forces (SkT6, SkO, SkM*, SIII, SGII, SLy4, SLy6, SkI3). Time-odd densities are essential for maintaining the Galilean invariance of the Skyrme functional. Their contribution is determined by the values and signs of the isovector and isoscalar effective-mass parameters of the force. In even-even nuclei these densities are not active in the ground state but can affect the dynamics. As a particular case, we explore the role of the current density in the description of isovector E1 and isoscalar E2 giant resonances in a chain of spherical and deformed Nd isotopes with A=134-158. The relation of the current to the effective masses and relevant parameters of the Skyrme functional is analyzed. It is shown that the current contributes substantially to E1 and E2 and the contribution is the same for all the isotopes along the chain, i.e. for both standard and exotic nuclei.

ORBITAL MAGNETIC DIPOLE MODE IN DEFORMED CLUSTERS : A FULLY MICROSCOPIC ANALYSIS

The orbital M1 collective mode predicted for deformed clusters in a schematic model is studied in a self-consistent random-phase-approximation approach which fully exploits the shell structure of the clusters. The microscopic mechanism of the excitation is clarified and the close correlation with E2 mode established. The study shows that the M1 strength of the mode is fragmented over a large energy interval. In spite of that, the fraction remaining at low energy, well below the overwhelming dipole plasmon resonance, is comparable to the strength predicted in the schematic model. The importance of this result in view of future experiments is stressed.

Giant dipole resonance in deformed nuclei: dependence on Skyrme forces

The giant dipole resonance (GDR) in deformed nuclei is analyzed using the self-consistent separable random-phase-approximation (SRPA) with Skyrme forces SkT6, SkM*, SLy6 and SkI3. The deformed nuclei 150Nd and 238U are used as representative rare-earth and actinide samples. Dependences of the dipole strength distributions on some basic characteristics of the Skyrme functional and nuclear matter properties (isoscalar and isovector effective masses, time-odd contributions) are discussed. Particular attention is paid to the fragmentation structure of the GDR strength which is shown to depend sensitively to spin-orbit intruder states with large angular momentum.

SKYRME-RANDOM-PHASE-APPROXIMATION DESCRIPTION OF E1 STRENGTH IN 92–100Mo

The isovector dipole E1 strength in 92,94,96,98,100Mo is analyzed within the self-consistent separable random-phase approximation (SRPA) model with Skyrme forces SkT6, SkM*, SLy6, and SkI3. The special attention is paid to the low-energy region near the particle thresholds (4-12 MeV), which is important for understanding of astrophysical processes. We show that, due to a compensation effect, the influence of nuclear deformation on E1 strength below 10-12 MeV is quite modest. At the same time, in agreement with previous predictions, the deformation increases the strength at higher energy. At 4-8 MeV the strength is mainly determined by the tail of E1 giant resonance. The four Skyrme forces differ in description of the whole giant resonance but give rather similar results below 12 MeV.

Electric Multipole Plasmons in Deformed Sodium Clusters

Abstract The random-phase-approximation (RPA) method with separable residual forces (SRPA) is proposed for the description of multipole electric oscillations of valence electrons in deformed alkali metal clusters. Both the deformed mean field and residual interaction are derived self-consistently from the Kohn–Sham functional. SRPA drastically simplifies the computational effort which is urgent if not decisive for deformed systems. The method is applied to the description of dipole, quadrupole, and octupole plasmons in deformed sodium clusters of a moderate size. We demonstrate that, in clusters with the size N>50, Landau damping successfully competes with deformation splitting and even becomes decisive in forming the width and gross structure of the dipole plasmon. Besides, the plasmon is generated by excitations from both ground state and shape isomers. In such clusters familiar experimental estimates for deformation splitting of dipole plasmon are useless.

Toroidal resonance: Relation to pygmy mode, vortical properties, and anomalous deformation splitting

We review a recent progress in investigation of the isoscalar toroidal dipole resonance (TDR). A possible relation of the TDR and low-energy dipole excitations (also called a pygmy resonance) is analyzed. It is shown that the dipole strength in the pygmy region can be understood as a local manifestation of the collective vortical toroidalmotion at the nuclear surface. Application of the TDR as a measure of the nuclear dipole vorticity is discussed. An anomalous splitting of the TDR in deformed nuclei is inspected.

SKYRME–HARTREE–FOCK DESCRIPTION OF THE DIPOLE STRENGTH IN NEUTRON-RICH TIN ISOTOPES

Low-energy E1 strength in neutron-rich 132-164Sn isotopes is analyzed in the framework of the Skyrme random phase approximation (RPA) with different Skyrme forces. A double folding procedure is applied to take into account the energy-dependent width effects beyond RPA. All the considered Skyrme forces indicate a soft prolate deformation in the open shell isotopes 142-164Sn. The integrated E1 strength in the energy region of the pygmy resonance grows with the neutron number. The influence of deformation on the integrated strength near the particle emission thresholds (which is of a keen astrophysical interest) is strictly suppressed by the mutual compensation effect for the branches of the giant dipole resonance. The results obtained are in a good agreement with the previous findings of the relativistic mean field model.

Toroidal, compression, and vortical dipole strengths in 144-154Sm: Skyrme-RPA exploration of the deformation effect

A comparative analysis of toroidal, compressional and vortical dipole strengths in the spherical 144Sm and the deformed 154Sm is performed within the random-phase approximation using a set of different Skyrme forces. Isoscalar (T = 0, isovector (T = 1 , and electromagnetic excitation channels are considered. The role of the nuclear convection

CollectiveEλ excitations of surface character in spherical and deformed sodium clusters: vibrating potential model

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