arXiv subjects

G. A. Lalazissis

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

72 records · Page 4Linked to original sources

arXiv1997

Relativistic Hartree-Bogoliubov description of the neutron drip-line in light nuclei

The Relativistic Hartree Bogoliubov theory is applied in the mean-field approximation to the description of properties of light nuclei with large neutron excess. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Using standard parameter sets for the mean-field Lagrangian and the pairing interaction of Gogny-type, self-consistent solutions in coordinate space are calculated for the ground states of a number of neutron-rich nuclei. The model predicts the location of the neutron drip-line, reduction of the spin-orbit interaction, $rms$ radii, changes in surface properties, the formation of neutron skin and of neutron halo.

nucl-th↗

arXiv1997

Relativistic mean-field description of light $Λ$ hypernuclei with large neutron excess

The Relativistic Hartree Bogoliubov model in coordinate space, with finite range pairing interaction, is applied to the description of $Λ$-hypernuclei with a large neutron excess. The addition of the $Λ$ hyperon to Ne isotopes with neutron halo can shift the neutron drip by stabilizing an otherwise unbound core nucleus. The additional binding of the halo neutrons to the core originates from the increase in magnitude of the spin-orbit term. Although the $Λ$ produces only a fractional change in the central mean-field potential, through a purely relativistic effect it increases the spin-orbit term which binds the outermost neutrons.

nucl-th↗

arXiv1997

Relativistic Hartree-Bogoliubov theory with finite range pairing forces in coordinate space: Neutron halo in light nuclei

The Relativistic Hartree Bogoliubov (RHB) model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the s-d shell. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Finite element methods are used in the coordinate space discretization of the coupled system of Dirac-Hartree-Bogoliubov integro-differential eigenvalue equations, and Klein-Gordon equations for the meson fields. Calculations are performed for the isotopic chains of Ne and C nuclei. We find evidence for the occurrence of neutron halo in heavier Ne isotopes. The properties of the 1f-2p orbitals near the Fermi level and the neutron pairing interaction play a crucial role in the formation of the halo. Our calculations display no evidence for the neutron halo phenomenon in C isotopes.

nucl-th↗

arXiv1997

Reduction of the spin-orbit potential in light drip-line nuclei

The isospin dependence of the spin-orbit interaction in light neutron rich nuclei is investigated in the framework of relativistic mean field theory. The magnitude of the spin-orbit potential is considerably reduced in drip line nuclei, resulting in smaller energy splittings between spin-orbit partners. The effect does not depend on the parametrization of the effective Lagrangian. The results are compared with corresponding calculations in the non-relativistic Skyrme model.

nucl-th↗

arXiv1997

Ground state properties of the $β$ stable nuclei in various mean field theories

The separation energies of neutrons and protons, binding energies, mean square charge radii, electric quadrupole moments and deformation parameters of the proton and neutron distributions are evaluated for $β$ stable even-even nuclei with $16 \leq A \leq 256$. We compare the theoretical estimates obtained within the Hartree-Fock plus BCS model with a few sets of Skyrme forces, relativistic mean-field theory and frequently used Saxon-Woods and Nilsson potentials with experimental data.

nucl-th↗

arXiv1997

Symmetries in nuclei and molecules

Recent progress in two different fronts is reported. First, the concept of bisection of a harmonic oscillator (HO) or hydrogen atom (HA), used in the past in establishing the connection between U(3) and O(4), is generalized into multisection (trisection, tetrasection, etc). It is then shown that all symmetries of the N-dim anisotropic HO with rational ratios of frequencies (RHO), some of which are underlying the structure of superdeformed and hyperdeformed nuclei, can be obtained from the U(N) symmetry of the corresponding isotropic HO with an appropriate combination of multisections. Furthermore, it is seen that bisections of the N-dim HA, which possesses an O(N+1) symmetry, lead to the U(N) symmetry, so that further multisections of the HA lead to the symmetries of the N-dim RHO. Second, it is shown that there is evidence that the recently observed in superdeformed nuclear bands $ΔI=4$ bifurcation is also occuring in rotational bands of diatomic molecules. In addition there is evidence that a $ΔI=8$ bifurcation, of the same order of magnitude as the $ΔI=4$ one, is observed in superdeformed nuclear bands and rotational bands of diatomic molecules.

nucl-th↗

arXiv1996

Monopole giant resonances and nuclear compressibility in relativistic mean field theory

Isoscalar and isovector monopole oscillations that correspond to giant resonances in spherical nuclei are described in the framework of time-dependent relativistic mean-field (RMF) theory. Excitation energies and the structure of eigenmodes are determined from a Fourier analysis of dynamical monopole moments and densities. The generator coordinate method, with generating functions that are solutions of constrained RMF calculations, is also used to calculate excitation energies and transition densities of giant monopole states. Calculations are performed with effective interactions which differ in their prediction of the nuclear matter compression modulus K_nm. Both time-dependent and constrained RMF results indicate that empirical GMR energies are best reproduced by an effective force with K_nm \approx 270 MeV.

nucl-th↗

arXiv1996

$ΔI=4$ and $ΔI=8$ bifurcations in rotational bands of diatomic molecules

It is shown that the recently observed $ΔI=4$ bifurcation seen in superdeformed nuclear bands is also occurring in rotational bands of diatomic molecules. In addition, signs of a $ΔI=8$ bifurcation, of the same order of magnitude as the $ΔI=4$ one, are observed both in superdeformed nuclear bands and rotational bands of diatomic molecules.

chem-ph↗

arXiv1996

Superheavy Nuclei in the Relativistic Mean Field Theory

We have carried out a study of superheavy nuclei in the framework of the Relativistic Mean-Field theory. Relativistic Hartree-Bogoliubov (RHB) calculations have been performed for nuclei with large proton and neutron numbers. A finite-range pairing force of Gogny type has been used in the RHB calculations. The ground-state properties of very heavy nuclei with atomic numbers Z=100-114 and neutron numbers N=154-190 have been obtained. The results show that in addition to N=184 the neutron numbers N=160 and N=166 exhibit an extra stability as compared to their neighbors. For the case of protons the atomic number Z=106 is shown to demonstrate a closed-shell behavior in the region of well deformed nuclei about N=160. The proton number Z=114 also indicates a shell closure. Indications for a doubly magic character at Z=106 and N=160 are observed. Implications of shell closures on a possible synthesis of superheavy nuclei are discussed.

nucl-th↗

arXiv1996

A New Parameterization for the Lagrangian Density of Relativistic Mean Field Theory

A new parameterization for an effective non-linear Lagrangian density of relativistic mean field (RMF) theory is proposed, which is able to provide an excellent description not only for the properties of stable nuclei but also for those far from the valley of beta-stability. In addition recently measured superdeformed mimima in the Hg-region are reproduced with high accuracy.

nucl-th↗

arXiv1996

Analysis of Delta I =2 staggering in nuclear rotational spectra

A method is proposed and tested for the analysis of Delta I=2 staggering observed in nuclear rotational bands. We examine six super- and hyper-deformed bands, among which that of 149Gd and possibly of 147Gd seem to exhibit real staggering. However, we emphasize that the presence of staggering may not necessarily imply the occurrence of bifurcation. It is also shown that a similar staggering seen in normally deformed bands is a manifestation of band crossings. A more extensive analysis is planned.

nucl-th↗

arXiv1996

Effects of Short Range Correlations on Ca Isotopes

The effect of Short Range Correlations (SRC) on Ca isotopes is studied using a simple phenomenological model. Theoretical expressions for the charge (proton) form factors, densities and moments of Ca nuclei are derived. The role of SRC in reproducing the empirical data for the charge density differences is examined. Their influence on the depletion of the nuclear Fermi surface is studied and the fractional occupation probabilities of the shell model orbits of Ca nuclei are calculated. The variation of SRC as function of the mass number is also discussed.

nucl-th↗

arXiv1995

Rare-Earth Nuclei: Radii, Isotope-Shifts and Deformation Properties in the Relativistic Mean Field Theory

A systematic study of the ground-state properties of even-even rare earth nuclei has been performed in the framework of the Relativistic Mean-Field (RMF) theory using the parameter set NL-SH. Nuclear radii, isotope shifts and deformation properties of the heavier rare-earth nuclei have been obtained, which encompass atomic numbers ranging from Z=60 to Z=70 and include a large range of isospin. It is shown that RMF theory is able to provide a good and comprehensive description of the empirical binding energies of the isotopic chains. At the same time the quadrupole deformations $β_{2}$ obtained in the RMF theory are found to be in good agreement with the available empirical values. The theory predicts a shape transition from prolate to oblate for nuclei at neutron number N=78 in all the chains. A further addition of neutrons up to the magic number 82 brings about the spherical shape. For nuclei above N=82, the RMF theory predicts the well-known onset of prolate deformation at about N=88, which saturates at about N=102. The deformation properties display an identical behaviour for all the nuclear chains. A good description of the above deformation transitions in the RMF theory in all the isotopic chains leads to a successful reproduction of the anomalous behaviour of the empirical isotopic shifts of the rare-earth nuclei. The RMF theory exhibits a remarkable success in providing a unified and microscopic description of various empirical data.

nucl-th↗

arXiv1995

Ground state properties of exotic nuclei near Z=40 in the relativistic mean-field theory,

Study of the ground-state properties of Kr, Sr and Zr isotopes has been performed in the framework of the relativistic mean field (RMF) theory using the recently proposed relativistic parameter set NL-SH. It is shown that the RMF theory provides an unified and excellent description of the binding energies, isotope shifts and deformation properties of nuclei over a large range of isospin in the Z=40 region. It is observed that the RMF theory with the force NL-SH is able to describe the anomalous kinks in isotope shifts in Kr and Sr nuclei, the problem which has hitherto remained unresolved. This is in contrast with the density-dependent Skyrme Hartree-Fock approach which does not reproduce the behaviour of the isotope shifts about shell closure. On the Zr chain we predict that the isotope shifts exhibit a trend similar to that of the Kr and Sr nuclei. The RMF theory also predicts shape coexistence in heavy Sr isotopes. Several dramatic shape transitions in the isotopic chains are shown to be a general feature of nuclei in this region. A comparison of the properties with the available mass models shows that the results of the RMF theory are generally in accord with the predictions of the finite-range droplet model.

nucl-th↗

arXiv1994

Isospin Dependence of the Spin-Orbit Force and Effective Nuclear Potentials

The isospin dependence of the spin-orbit potential is investigated for an effective Skyrme like energy-functional suitable for density-dependent Hartree-Fock calculations. The magnitude of the isospin dependence is obtained from a fit to experimental data on finite spherical nuclei. It is found to be close to that of relativistic Hartree models. Consequently the anomalous kink in the isotope shifts of Pb nuclei is well reproduced.

nucl-th↗

arXiv1994

Anomalous Isotope Shifts in Pb Nuclei in RMF Theory

We have studied the anomalous behaviour of isotopic shifts of Pb nuclei in the relativistic mean field theory. It has been shown that the relativistic mean field provides an excellent description of the anomalous kink in the isotopic shifts about $^{208}$Pb. This is in contrast from density-dependent Skyrme forces which do not reproduce the observed trend in the empirical data on the charge radii. We discuss some differences in the description of isotope shifts in the RMF theory and the Skyrme mean field.

nucl-th↗

arXiv1993

Shell Effects in Nuclei Near Neutron Drip

Shell effects in nuclei close to the neutron-drip lines have been investigated. It has been demonstrated in the relativistic mean-field theory that nuclei very far from stability manifest the shell effects strongly. This behaviour is in accord with the predictions of nuclear masses in the finite-range droplet model including shell corrections. As a consequence we find a large neutron halo in nuclei near the neutron-drip line. The shell effects predicted in the existing Skyrme mean-field theory in comparison are significantly weaker than those of the other approaches.

nucl-th↗

arXiv1993

Anomaly in the charge radii of Pb isotopes

The anomalous behaviour of the charge radii of the isotopic chain of Pb nuclei has been studied in the relativistic mean field theory. It has been shown that the relativistic mean field provides an excellent description of the anomalous kink in the isotopic shifts about $^{208}$Pb. This contrasts strongly from the Skyrme mean field, where almost all the known and realistic forces fail to reproduce the observed trend in the empirical data on the charge radii. The results have been discussed in the perspective of differences in the ansätze of the relativistic and the Skyrme mean-field theories.

nucl-th↗