No abstract

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.PACS numbers : 21.60Cs, 21.10. Dr, 21.10.Gv The Hartree-Fock approach based upon phenomenological density dependent forces [1,2,3] has proved to be very successful in the microscopic description of ground state properties of nuclear matter and of finite nuclei over the entire periodic table. In all these calculations the spin-orbit potential has been assumed to be isospin independent. Its only parameter, the strength, is usually adjusted to the experimental spin-orbit splitting in spherical nuclei like 16 O or 208 Pb. The exchange term, however, causes for nuclei with neutron excess a strong isospin dependence of the corresponding single-particle spin-orbit field.In recent years Relativistic Mean Field (RMF) theory [4] with nonlinear self-interactions between the mesons has gained considerable interest for the investigations of low-energy phenomena in nuclear structure. With only a few phenomenological parameters such theories are able to give a quantitative description of ground state properties of spherical and deformed nuclei [5,6] at and away from the stability line. In addition, excellent agreement with experimental data has been found recently also for collective excitations such as giant resonances [7] and for twin bands in rotating superdeformed nuclei [8]. In many respects the relativistic mean-field theory is regarded as similar to the density-dependent Hartree-Fock theory of the Skyrme type [9,10] Recently, however, detailed investigations of high precision data on nuclear charge radii in Pb isotopes [11,12] and of shell effects at the neutron drip line [13,14] have shown considerable differences between the Skyrme approach and the relativistic mean field theory. In fact, density dependent Hartree-Fock calculations with Skyrme [11] or Gogny forces [15], which used so far antisymmetrized, isospin independent spin-orbit interactions, were not able to reproduce the kink in the isotope shifts of Pb nuclei (see Fig. 1). On the other hand, this kink is obtained in the RMF theory without any new ad-justment of parameters [12]. Another considerable difference has been found in theoretical investigation of shell effects in very exotic Zr-isotopes near the neutron drip line: in conventional non-relativistic Skyrme calculations the shell gap at isotope 122 Zr with the magic neutron configuration N = 82 is totally smeared out [13], whereas relativistic calculations using various parameter sets show at N=82 a clear kink in the binding energy as a function of the neutron number [14]. This difference is caused by the different spin-orbit splitting of the single particle levels in these n...

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 ans\"atze of the relativistic and the Skyrme mean-field theories.Comment: 10 pages (Latex) and 3 figures (avilable upon request); Phys. Lett. B (in print), TUM-ITP-SH93/

No abstract

We have carried out a study of superheavy nuclei in the framework of the Rel-

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes 124−145 Sn and 208−238 Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orders * Permanent address: P. Moller

In recent years, nanoscience and nanotechnology have emerged as a new area of fundamental science and are receiving global attention due to their extensive applications. Conventionally nanoparticles were manufactured by physical and chemical techniques. The recent development and implementation of new technologies have led to a new trend, the nano-revolution unfolding the role of plants in bio-and green synthesis of nanoparticles which seems to have drawn a quite unequivocal attention to the synthesis of stable nanoparticles. Although nanoparticles can be synthesized through many conventional methods, biological route of the synthesis is more competent than the physical and chemical techniques. Biologically synthesized nanoparticles have enjoyed an upsurge of applications in various sectors. Hence, the present study envisions biosynthesis of nanoparticles from plants which are emerging as nanofactories. Hence, the present review summarizes the literature reported thus far and envisions plants as emerging sources of nanofactories along with applications, the mechanism behind phytosynthesis of nanoparticles and the mechanism of antibacterial action of nanoparticles.

Shell effects in nuclei about the stability line are investigated within the framework of the Relativistic Hartree-Bogoliubov (RHB) theory with self-consistent finiterange pairing. Using 2-neutron separation energies of Ni and Sn isotopes, the role of σ-and ω-meson couplings on the shell effects in nuclei is examined. It is observed that the existing successful nuclear forces (Lagrangian parameter sets) based upon the nonlinear scalar coupling of σ-meson exhibit shell effects which are stronger than suggested by the experimental data. We have introduced nonlinear vector self-coupling of ω-meson in the RHB theory. It is shown that the inclusion of the vector self-coupling of ω-meson in addition to the nonlinear scalar coupling of σ-meson provides a good agreement with the experimental data on shell effects in nuclei about the stability line. A comparison of the shell effects in the RHB theory is made with the Hartree-Fock Bogoliubov approach using the Skyrme force SkP. It is shown that the oft-discussed shell quenching with SkP is not consistent with the available experimental data.