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G. A. Lalazissis

Publications and source records attributed to G. A. Lalazissis.

At least 55 records · Page 3Linked to original sources

Relativistic mean-field description of nuclei at the drip lines

We present a review of recent applications of the relativistic mean-field theory to the structure of nuclei close to the drip-lines. For systems with extreme isospin values, the relativistic Hartree-Bogoliubov model provides a unified and self-consistent description of mean-field and pairing correlations. The model has been applied in studies of structure phenomena that include: formation of neutron skin and of neutron halos in light nuclei in the mass region above the s-d neutron shell, the strong isospin dependence of the effective spin-orbit interaction and the resulting modification of surface properties, the suppression of the spherical N=28 shell gap for neutron-rich nuclei and the related phenomenon of deformation and shape coexistence, the proton drip-line in the spherical nuclei $14\leq Z \leq 28$, and ground-state proton radioactivity in the region of deformed nuclei $59 \leq Z \leq 69$.

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Relativistic mean-field description of the dynamics of giant resonances

The relativistic mean-field theory provides a framework in which the nuclear many-body problem is described as a self-consistent system of nucleons and mesons. In the mean-field approximation, the self-consistent time evolution of the nuclear system describes the dynamics of collective motion: nuclear compressibility from monopole resonances, regular and chaotic dynamics of isoscalar and isovector collective vibrations.

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Relativistic Hartree-Bogoliubov description of the deformed ground-state proton emitters

Ground-state properties of deformed proton-rich odd-Z nuclei in the region $59 \leq Z \leq 69$ are described in the framework of Relativistic Hartree Bogoliubov (RHB) theory. One-proton separation energies and ground-state quadrupole deformations that result from fully self-consistent microscopic calculations are compared with available experimental data. The model predicts the location of the proton drip-line, the properties of proton emitters beyond the drip-line, and provides information about the deformed single-particle orbitals occupied by the odd valence proton.

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Nonlinear dynamics of giant resonances in atomic nuclei

The dynamics of monopole giant resonances in nuclei is analyzed in the time-dependent relativistic mean-field model. The phase spaces of isoscalar and isovector collective oscillations are reconstructed from the time-series of dynamical variables that characterize the proton and neutron density distributions. The analysis of the resulting recurrence plots and correlation dimensions indicate regular motion for the isoscalar mode, and chaotic dynamics for the isovector oscillations. Information-theoretic functionals identify and quantify the nonlinear dynamics of giant resonances in quantum systems that have spatial as well as temporal structure.

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Relativistic Hartree-Bogoliubov description of the deformed N = 28 region

Ground-state properties of neutron-rich $N \approx 28$ nuclei are described in the framework of Relativistic Hartree Bogoliubov (RHB) theory. The model uses the NL3 effective interaction in the mean-field Lagrangian, and describes pairing correlations by the pairing part of the finite range Gogny interaction D1S. Two-neutron separation energies and ground-state quadrupole deformations that result from fully self-consistent RHB solutions, are compared with available experimental data. The model predicts a strong suppression of the spherical N=28 shell gap for neutron-rich nuclei: the $1f7/2 \to fp$ core breaking results in deformed ground states. Shape coexistence is expected for neutron-rich Si, S and Ar isotopes.

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Proton drip-line nuclei in relativistic mean-field theory

The position of the two-proton drip line has been calculated for even-even nuclei with $10 \leq Z \leq 82$ in the framework of the relativistic mean-field (RMF) theory. The current model uses the NL3 effective interaction in the mean-field Lagrangian and describes pairing correlations in the Bardeen-Cooper-Schrieffer (BCS) formalism. The predictions of the RMF theory are compared with those of the Hartree-Fock+BCS approach (with effective force Skyrme SIII) and the finite-range droplet model (FRDM) and with the available experimental information.

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Relativistic Mean Field Approach and the Pseudo-Spin Symmetry

Based on the Relativistic Mean Field (RMF) approach the existence of the broken pseudo-spin symmetry is investigated. Both spherical RMF and constrained deformed RMF calculations are carried out employing realistic Lagrangian parameters for spherical and for deformed sample nuclei. The quasi - degenerate pseudo-spin doublets are confirmed to exist near the fermi surface for both spherical and deformed nuclei.

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Solution of relativistic Hartree-Bogoliubov equations in configurational representation: spherical neutron halo nuclei

The scaled harmonic oscillator basis (SHO) is derived by a local scaling-point transformation of the spherical harmonic oscillator radial wave functions. The unitary scaling transformation produces a basis with improved asymptotic properties. The SHO basis is employed in the solution of the relativistic Hartree-Bogoliubov (RHB) equations in configurational space. The model is applied in the self-consistent mean-field approximation to the description of the neutron halo in Ne isotopes. It is shown that an expansion of nucleon spinors and mean-field potentials in the SHO basis reproduces the asymptotic properties of neutron densities calculated by finite element discretization in the coordinate space. In the RHB description of neutron skins and halos, SHO bases in two or three dimensions can be a useful alternative to technically complicated solutions on a mesh in coordinate space.

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Relativistic Mean Field Theory in Rotating Frame: Single-particle Properties at Superdeformation

Single-particle properties at superdeformation are investigated within the Cranked Relativistic Mean Field (CRMF) theory on the example of superdeformed rotational bands observed in the A~140-150 mass region. Applying the effective alignment approach it is shown that CRMF theory provides a reasonable description of the alignment properties of the single-particle orbitals. The agreement with experiment is good in most of the cases. This suggests that many features of the observed superdeformed bands can be well understood in terms of an almost undisturbed single-particle motion. The stability of the results with respect to the parameterizations used in Relativistic Mean Field (RMF) theory is also investigated, employing some frequently used non-linear effective forces. It turns out, with the exception of the single-particle ordering in superdeformed minimum, that the dependence of the calculated observables on the parameterization is rather small.

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Proton drip-line nuclei in Relativistic Hartree-Bogoliubov theory

Ground-state properties of spherical even-even nuclei $14\leq Z \leq 28$ and $N=18,20,22$ are described in the framework of Relativistic Hartree Bogoliubov (RHB) theory. The model uses the NL3 effective interaction in the mean-field Lagrangian, and describes pairing correlations by the pairing part of the finite range Gogny interaction D1S. Binding energies, two-proton separation energies, and proton $rms$ radii that result from fully self-consistent RHB solutions are compared with experimental data. The model predicts the location of the proton drip-line. The isospin dependence of the effective spin-orbit potential is discussed, as well as pairing properties that result from the finite range interaction in the $pp$ channel.

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Analysis of the superdefomed rotational bands

All available experimental data for the $ΔI=2$ transition energies in superdeformed bands are analyzed by using a new one-point formula. The existence of deviations from the smooth behavior is confirmed in many bands. However, we stress that one cannot necessarily speak about staggering patterns as they are mostly irregular. Simulations of the experimental data suggest that the irregularities may stem from the presence of irregular kinks in the rotational spectra. This could be a clue but, at the moment, where such kinks come from is an open question.

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Analysis of Molecular Rotational Spectra

Rotational spectra of diatomic molecules measured in the high-precision experiments are analyzed. Such a spectrum is usually fitted by an 8th order polynomial in spin. In fact, from the theoretical point of view, the rotational spectrum is expected to be a smooth function of spin. Thus, fitting the rotational spectrum in terms of a low order polynomial in spin seems to be justified. However, this is not what we found in the present work. We show that the measured spectrum is not necessarily a smooth function of the spin, which is quite surprising. Whether or not it indicates the presence of some hidden physics is an open question.

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Relativistic Hartree-Bogoliubov description of ground-state properties of Ni and Sn isotopes

The Relativistic Hartree Bogoliubov (RHB) theory is applied in the description of ground-state properties of Ni and Sn isotopes. The NL3 parameter set is used for the effective mean-field Lagrangian, and pairing correlations are described by the pairing part of the finite range Gogny interaction D1S. Fully self-consistent RHB solutions are calculated for the Ni ($28\leq N\leq 50$) and Sn ($50\leq N\leq 82$) isotopes. Binding energies, neutron separation energies, and proton and neutron $rms$ radii are compared with experimental data. The model predicts a reduction of the spin-orbit potential with the increase of the number of neutrons. The resulting energy splittings between spin-orbit partners are discussed, as well as pairing properties calculated with the finite range effective interaction in the $pp$ channel.

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Excitation energy of superdeformed bands in Relativistic Mean Field Theory

Constrained Relativistic Mean Field (RMF) calculations have been carried out to estimate excitation energies relative to the ground state for superdeformed bands in the mass regions A $\sim$ 190 and A $\sim$ 150. It is shown that RMF theory is able to successfully reproduce the recently measured superdeformed minima in Hg and Pb nuclei.

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Information entropy as a measure of the quality of a nuclear density distribution

The information entropy of a nuclear density distribution is calculated for a number of nuclei. Various phenomenological models for the density distribution using different geometry are employed. Nuclear densities calculated within various microscopic mean field approaches are also employed. It turns out that the entropy increases on going from crude phenomenological models to more sophisticated (microscopic) ones. It is concluded that the larger the information entropy, the better the quality of the nuclear density distribution. An alternative approach is also examined: the net information content i.e. the sum of information entropies in position and momentum space $S_{r}+S_{k}$. It is indicated that $S_{r}+S_{k}$ is a maximum, when the best fit to experimental data of the density and momentum distributions is attained.

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Light Nuclei near Neutron and Proton Drip Lines in the Relativistic Mean-Field Theory

We have made a detailed study of the ground-state properties of nuclei in the light mass region with atomic numbers Z=10-22 in the framework of the relativistic mean-field (RMF) theory. The nonlinear $σω$ model with scalar self-interaction has been employed. The RMF calculations have been performed in an axially deformed configuration using the force NL-SH. We have considered nuclei about the stability line as well as those close to proton and neutron drip lines. It is shown that the RMF results provide a good agreement with the available empirical data. The RMF predictions also show a reasonably good agreement with those of the mass models. It is observed that nuclei in this mass region are found to possess strong deformations and exhibit shape changes all along the isotopic chains. The phenomenon of the shape coexistence is found to persist near the stability line as well as near the drip lines. It is shown that the magic number N=28 is quenched strongly, thus enabling the corresponding nuclei to assume strong deformations. Nuclei near the neutron and proton drip lines in this region are also shown to be strongly deformed.

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Computer program for the relativistic mean field description of the ground state properties of even-even axially deformed nuclei

A Fortran program for the calculation of the ground state properties of axially deformed even-even nuclei in the relativistic framework is presented. In this relativistic mean field (RMF) approach a set of coupled differential equations namely the Dirac equation with potential terms for the nucleons and the Glein-Gordon type equations with sources for the meson and the electromagnetic fields are to be solved self-consistently. The well tested basis expansion method is used for this purpose. Accordingly a set of harmonic oscillator basis generated by an axially deformed potential are used in the expansion. The solution gives the nucleon spinors, the fields and level occupancies, which are used in the calculation of the ground state properties.

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Cranked Relativistic Mean Field Description of Superdeformed Rotational Bands

The cranked relativistic mean field theory is applied for a detailed investigation of eight superdeformed rotational bands observed in $^{151}$Tb. It is shown that this theory is able to reproduce reasonably well not only the dynamic moments of inertia $J^{(2)}$ of the observed bands but also the alignment properties of the single-particle orbitals.

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