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.Comment: 8 Pages, LateX, 4 P.S. Figures, submit. Phys. Lett.

On the Thermodynamic Limit of the Lipkin Model

The thermodynamic limit of the Lipkin model is investigated. While the limit turns out to be rather elusive, the analysis gives strong indications that the limit yields two analytically dissociated operators, one for the normal and one for the deformed phase. While the Lipkin Hamiltonian is hermitian and has a second order phase transition in finite dimensions (finite particle number), both properties seem to be destroyed in the thermodynamic limit.Comment: 9 pages, 3 figures to appear in JPhys

Microscopic calculation of 240Pu scission with a finite-range effective force

Hartree-Fock-Bogoliubov calculations of hot fission in $^{240}\textrm{Pu}$ have been performed with a newly-implemented code that uses the D1S finite-range effective interaction. The hot-scission line is identified in the quadrupole-octupole-moment coordinate space. Fission-fragment shapes are extracted from the calculations. A benchmark calculation for $^{226}\textrm{Th}$ is obtained and compared to results in the literature. In addition, technical aspects of the use of HFB calculations for fission studies are examined in detail. In particular, the identification of scission configurations, the sensitivity of near-scission calculations to the choice of collective coordinates in the HFB iterations, and the formalism for the adjustment of collective-variable constraints are discussed. The power of the constraint-adjustment algorithm is illustrated with calculations near the critical scission configurations with up to seven simultaneous constraints.Comment: 18 pages, 24 figures, to be published in Physical Review

Relativistic Hartree-Bogoliubov theory in coordinate space: finite element solution for a nuclear system with spherical symmetry

A C++ code for the solution of the relativistic Hartree-Bogoliubov theory in coordinate space is presented. The theory describes a nucleus as a relativistic system of baryons and mesons. The RHB model is applied in the self-consistent mean-field approximation to the description of ground state properties of spherical nuclei. Finite range interactions are included to describe pairing correlations and the coupling to particle continuum states. 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. The bisection method is used in the solution of the resulting generalized algebraic eigenvalue problem, and the biconjugate gradient method for the systems of linear and nonlinear algebraic equations, respectively.Comment: PostScript, 32 pages, to be published in Computer Physics Communictions (1997

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.Comment: 30 pages of LaTeX, 18 PS-figure

Time-odd mean fields in the rotating frame: microscopic nature of nuclear magnetism

The microscopic role of nuclear magnetism in rotating frame is investigated for the first time in the framework of the cranked relativistic mean field theory. It is shown that nuclear magnetism modifies the expectation values of single-particle spin, orbital and total angular momenta along the rotational axis effectively creating additional angular momentum. This effect leads to the increase of kinematic and dynamic moments of inertia at given rotational frequency and has an impact on effective alignments.Comment: 16 pages, 4 figures, submitted to Physical Review

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.Comment: 7 pages, Latex, 5 P.S. Figures, To appear in Phys. Rev. Let

Economic Analysis of Insect Control Strategies Using an Integrated Crop Ecosystem Management Model

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 8 (2006): Economic Analysis of Insect Control Strategies Using an Integrated Crop Ecosystem Management Model. Manuscript IT 06 001. Vol. VIII. September, 2006

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.Comment: 11 pages, RevTex, 12 p.s figures, submitted to Phys. Rev.