Light nuclei near neutron and proton drip lines in 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 good agreement with the available empirical data. The RMF predictions also show 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 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.     

Halo nuclei studied by relativistic mean-field approach

Density distributions of light neutron-rich nuclei are studied by using the relativistic mean-field approach. The effective interaction which parameterizes the recent Dirac-Brueckner-Hartree-Fock calculations of nuclear matter is used. The results are discussed and compared with the experimental observations with special reference to theneutron halo in the drip-line nuclei.     

Shape Coexistence in Odd-Mass Nuclei near Z = 50

An earlier work dealing with shape coexistence for even-even nuclei is extended to treating odd-mass nuclei including proton excitations across closed shell. With the approach, energy spectra and some E2 transition branching ratios are calculated for odd-Anuclei^113~125Sb,^115~127I. The theoretical results give a good reproduction to the experimental data.     

Collective excitations of nuclei in a relativistic mean-field theory

Collective excitations of finite nuclei are discussed in a model relativistic baryon-meson field theory. Eigenvalue equations for small amplitude motion about the static mean-field solutions assuming irrotational flow are derived. Variational estimates of the lowest modes are obtained.     

Properties and structure of N=Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48.Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square (rms) radii of charge and neutron, and shell gaps have been calculated.The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42.The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43.The evolution of shell gaps with proton number Z can be clearly observed.Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region.In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.     

Properties and structure of N=Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square （rms） radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.     

Neutron halo in lithium nuclei: A relativistic mean-field approach

Relativistic mean-field calculations have been carried out for Li isotopes using the non-linear Lagrangian parameter set NL2. Both spherically symmetric and axially deformed cases are considered. The binding energies, charge, neutron and matterrms radii, one and two neutron separation energies have been calculated. The results are discussed and compared with the available non-relativistic mean-field results, with special reference toneutron halo in the recent experimental observations.     

Proton emission from the drip-line nuclei I-Bi using the WKB approximation with relativistic mean-field densities

crucial application to the existence of exotic nuclei. The effective relativistic meanfield formalism(E-RMF), with NL3, FSUGarnet, G3 and IOPB-I interactions, is adopted for analysis of the ground state properties of proton emitters. Furthermore, in the E-RMF background, the Wentzel-Karmers-Brillouin(WKB)barrier penetration method is used for the calculation of proton emission half-lives. It is found that the calculated halflives are in good agreement with the experimental results for all emitters considered in this study.     

Deuteron transfer in N=Z nuclei

Predictions are obtained for T=0 and T=1 deuteron-transfer intensities between self-conjugate N=Z nuclei on the basis of a simplified interacting boson model which considers bosons without orbital angular momentum but with full spin-isospin structure. These transfer predictions can be correlated with nuclear binding energies in specific regions of the mass table.     

Constrained relativistic mean-field approach with fixed configurations

A diabatic (configuration-fixed) constrained approach to calculate the potential energy surface (PES) of the nucleus is developed in the relativistic mean-field model. As an example, the potential energy surfaces of ²⁰⁸Pb obtained from both adiabatic and diabatic constrained approaches are investigated and compared. It is shown that the diabatic constrained approach enables one to decompose the segmented PES obtained in usual adiabatic approaches into separate parts uniquely characterized by different configurations, to follow the evolution of single-particle orbits till the very deformed region, and to obtain several well-defined deformed excited states which can hardly be expected from the adiabatic PESs.     

Level inversion of N=9 isotones in the relativistic mean-field theory

We have studied the ground state properties of N=8 and N=9 isotones in the framework of the nonlinear relativistic mean-field (RMF) theory using force parameters NL-SH. Calculations show that the RMF theory can describe experimental data of binding energies and radii for these nuclei. The RMF theory can also reproduce the level inversion of N=9 isotones well if the ρ tensor coupling is included. One-neutron halos in ¹⁵C and ¹⁴B are predicted.     

Production of exotic neutron-deficient isotopes near N,Z=50 in multinucleon transfer reactions

The multinucleon transfer reaction in the collisions of ~(40) Ca+ ~(124) Sn at Ec.m. = 128.5 MeV is investigated using the improved quantum molecular dynamics model. The measured angular distributions and isotopic distributions of the products are reproduced reasonably well by the calculations. The multinucleon transfer reactions of ~(40) Ca +~(112) Sn, ~(58) Ni + ~(112) Sn, ~(106) Cd + ~(112) Sn, and ~(48) Ca + ~(112) Sn are also studied. This demonstrates that the combinations of neutron-deficient projectile and target are advantageous for the production of exotic neutron-deficient nuclei near N,Z =50. The charged particles' emission plays an important role at small impact parameters in the de-excitation processes of the system. The production cross sections of the exotic neutron-deficient nuclei in multinucleon transfer reactions are much larger than those measured in the fragmentation and fusion-evaporation reactions. Several new neutron-deficient nuclei can be produced in the ~(106) Cd + ~(112) Sn reaction. The corresponding production cross sections for the new neutron-deficient nuclei,~(101,112) Sb,~(103) Te,and ~106,107) I,are 2.0 nb,4.1 nb,6.5 nb,0.4 μb and 1.0 μb,respectively.     

A systematic study of superheavy nuclei for Z = 114 and beyond using the relativistic mean field approach

We have studied the structural properties of even-even, neutron deficient, Z = 114–126, superheavy nuclei in the mass region A ∼ 270–320, using an axially deformed relativistic mean field model. The calculations are performed with three parameter sets (NL1, TM1 and NL-SH), in order to see the dependence of the structural properties on the force used. The calculated ground state shapes are found to be parameter dependent. For some parameter sets, many of the nuclei are degenerate in their ground state configuration. Special attention is given to the investigation of the magic structures (spherical shell closures) in the superheavy region. We find that some known magic numbers are absent and new closed shells are predicted. Large shell gaps appear at Z = 80, 92, (114), 120 and 138, N = 138, (164), (172), 184, (198), (228) and 258, irrespective of the parameter sets used. The numbers in parenthesis are those which correspond to relatively smaller gaps. The existence of new magic numbers in the valley of superheavy elements is discussed. It is suggested that nuclei around Z = 114 and N = 164 ∼ 172 could be considered as candidates for the next search of superheavy nuclei. The existence of superheavy islands around Z = 120 and N = 172 or N = 184 double shell closure is also discussed.     

Symmetry properties of radioactive N=Z nuclei

Recent mass measurements of proton-rich nuclei close to the N=Z line were used for the calculation of the interaction strength δV _pn between valence protons and neutrons. When compared with δV _pn values calculated from mass values of the AME’95 mass tables, the breaking down of the SU(4) symmetry is verified at Z=32,33,34.     

Low energyK + scattering onN =Z nuclei

The data for the total cross-section ofK ⁺ scattering on various nuclei have been analysed in the Glauber multiple scattering theory. Energy-dependentK ⁺ -nucleus optical potential is generated using the forwardK ⁺ -nucleon scattering amplitude and the nuclear density distribution. Along with this, the calculated totalK ⁺ -nucleus cross-sections using the effectiveK ⁺ -nucleon crosssection inside the nucleus are also presented.     

Shell-model calculations inA=28–32 nuclei

Shell-model calculations for positive-parity levels of A=28–32 nuclei have been performed in a 1d_5/2 2s_1/2 1d_3/2 configuration space. Configuration mixing of at most 250 lowest-lying pure configurations for each (A, J, T) set was taken into account. By a variation of the four effective interaction (MSDI) parameters and three single-particle energies a search was made for the best fit of the calculated energies to the experimental values. The average deviation between theory and experiment for the energies of the 110 fitted levels is 0.44 MeV. By adjusting all the 63 two-body matrix elements (ASDI) and the three single-particle energies, the average deviation of the binding energies was reduced to 0.16 MeV. For the lowest 10–15 levels in all A=28–32 nuclei a one to one correspondence exists between theory and experiment. Electromagnetic transition strengths were calculated both with MSDI and with ASDI wave functions. The ASDI wave functions reproduce the experimental E2 data much better than the MSDI wave functions. For the M1 transition strengths only a minor improvement has been achieved.