Shell-model studies on exotic nuclei around 132Sn

The study of exotic nuclei around 132Sn is a subject of current experimental and theoretical interest. Experimental information for nuclei in the vicinity of 132Sn, which have been long inaccessible to spectroscopic studies, is now available thanks to new advanced facilities and techniques. The experimental data which have been now become available for these neutron-rich nuclei may suggest a modification in the shell structure. They are, in fact, somewhat different from what one might expect by extrapolating the existing results for N<82, and as a possible explanation a change in the single-proton level scheme has been suggested. The latter would be caused by a more diffuse nuclear surface, and could be seen as a precursor of major effects which should show up at larger neutron excess. New data offer therefore the opportunity to test the shell model and look for a possible evolution of shell structure when going toward neutron drip line. This is stimulating shell-model studies in this region. Here, we present an overview of recent shell-model studies of 132Sn neighbors, focusing attention on those calculations employing realistic effective interactions.Comment: 8 pages, 4 tables, invited talk at INPC2007, Tokyo, Japan, June 3-8 2007. To be published in Nuclear Physics

Shell-model study of quadrupole collectivity in light tin isotopes

A realistic shell-model study is performed for neutron-deficient tin isotopes up to mass A=108. All shell-model ingredients, namely two-body matrix elements, single-particle energies, and effective charges for electric quadrupole transition operators, have been calculated by way of the many-body perturbation theory, starting from a low-momentum interaction derived from the high-precision CD-Bonn free nucleon-nucleon potential. The focus has been put on the enhanced quadrupole collectivity of these nuclei, which is testified by the observed large B(E2;0+ -> 2+)s. Our results evidence the crucial role played by the Z=50 cross-shell excitations that need to be taken into account explicitly to obtain a satisfactory theoretical description of light tin isotopes. We find also that a relevant contribution comes from the calculated neutron effective charges, whose magnitudes exceed the standard empirical values. An original double-step procedure has been introduced to reduce effectively the model space in order to overcome the computational problem.Comment: 6 pages, 6 figures, 2 table

Shell-Model Calculations with Realistic Effective Interactions

In this paper, we present some results of shell-model calculations employing effective interactions derived from the CD-Bonn free nucleon-nucleon potential. These concern 18O, 134Te, and 210Po, and are part of a comprehensive study of nuclei around doubly closed shells. Comparison of the calculated results with experimental data illustrates the degree of accuracy of modern realistic shell-model calculations.Comment: Talk presented at INPC 2001, 29 July - 3 August 2001, Berkeley (USA

Low-momentum Nucleon-Nucleon Potential and Hartree-Fock Calculations

A low-momentum nucleon-nucleon (NN) potential V-low-k is derived from modern realistic NN potentials by integrating out the high-momentum modes. The smooth V-low-k may be used as input for nuclear structure calculations instead of the usual Brueckner G matrix. Such an approach eliminates the energy dependence one finds in the G-matrix approach, allowing this interaction to be used directly in Hartree-Fock calculations. Bulk properties of 16O have been calculated starting from different NN potentials. Our results, obtained including up to second order contributions in the Goldstone expansion, are in good agreement with experiment.Comment: 7 pages, talk presented at IX Convegno su Problemi di Fisica Nucleare Teorica, Cortona (Italy), October 9-12 200

p-Shell Nuclei and Two-Frequency Shell Model with a Realistic Effective Interaction

We have studied p-shell nuclei using a two-frequency shell-model approach with an effective interaction derived from the Bonn-A nucleon-nucleon potential by means of a G-matrix folded-diagram method. First, we briefly describe our derivation of the effective interaction in a model space composed of harmonic hoscillator wave functions with two different length parameters, b_in and b_out, for the core and the valence orbits, respectively. Then we present some selected results of our calculations. We show that a good agreement with experiment is obtained, which is definitely better than that provided by a standard one-frequency calculation. A comparison with results obtained from large-basis shell-model calculations is also made.Comment: 9 pages, 1 figure, talk presented at VIII Convegno di Fisica Nucleare Teorica, Cortona, 18-21 Ottobre 200

Shell-model study of the N=82 isotonic chain with a realistic effective hamiltonian

We have performed shell-model calculations for the even- and odd-mass N=82 isotones, focusing attention on low-energy states. The single-particle energies and effective two-body interaction have been both determined within the framework of the time-dependent degenerate linked-diagram perturbation theory, starting from a low-momentum interaction derived from the CD-Bonn nucleon-nucleon potential. In this way, no phenomenological input enters our effective Hamiltonian, whose reliability is evidenced by the good agreement between theory and experiment.Comment: 7 pages, 11 figures, 3 tables, to be published in Physical Review

Low-momentum nucleon-nucleon interaction and shell-model calculations

We discuss the use of the low-momentum nucleon-nucleon NN interaction V-low-k in the derivation of the shell-model effective interaction and emphasize its practical value as an alternative to the Brueckner G-matrix method. We present some selected results of our current study of exotic nuclei around closed shells, which have been obtained starting from the CD-Bonn potential. We also show some results of calculations performed with different phase-shift equivalent NN potentials, and discuss the effect of changes in the cutoff momentum which defines the V-low-k potential.Comment: 5 pages, 5 figures, 1 table, Talk presented at CDN05, 31 Jan - 4 Feb 2005, University of Tokyo, Japa