arXiv subjects

A. Covello

Publications and source records attributed to A. Covello.

65 records · Page 4Linked to original sources

arXiv2000

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.

nucl-th↗

arXiv2000

Particle-Rotor Model Description of Doubly Odd Ta Isotopes

The doubly odd Ta isotopes are studied within the framework of the particle-rotor model. The main aim of this study is to obtain information on the neutron-proton interaction in deformed nuclei, with particular attention focused on the role of the tensor force. To this end, both zero-range abd finite-range phenomenological interactions are considered. Comparison of the calculated results with experimental data provides evidence of the importance of the tensor-force effects. We have also performed calculations using a realistic two-body G matrix for the neutron proton interaction. Some preliminary results are presented here.

nucl-th↗

arXiv2000

Present Status of Realistic Shell-Model Calculations

The present paper is comprised of two parts. First, we give a brief survey of the theoretical framework for microscopic nuclear structure calculations starting from a free nucleon-nucleon potential. Then, we present some selected results of a comprehensive study of nuclei near doubly closed shells. In all these shell-model calculations we have made use of realistic effective interactions derived from the Bonn-A nucleon-nucleon potential by means of a G-matrix folded-diagram method. We show that this kind of calculation yields a very good agreement with experiment for all the nuclei considered. This leads to the conclusion that realistic effective interactions are now able to describe with quantitative accuracy the properties of complex nuclei.

nucl-th↗

arXiv2000

Realistic Shell-Model Calculations for Proton-Rich N=50 Isotones

The structure of the N=50 isotones 98Cd, 97Ag, and 96Pd is studied in terms of shell model employing a realistic effective interaction derived from the Bonn-A nucleon-nucleon potential. The single-hole energies are fixed by resorting to an analysis of the low-energy spectra of the isotones with A>= 91. Comparison shows that our results are in very satisfactory agreement with the available experimental data. This supports confidence in the predictions of our calculations

nucl-th↗

arXiv1999

Bonn Potential and Shell-Model Calculations for N=126 Isotones

We have performed shell-model calculations for the N=126 isotones 210Po, 211At, and 212Rn using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential by means of a G-matrix folded-diagram method. The calculted binding energies, energy spectra and electromagnetic properties show remarkably good agreement with the experimental data. The results of this paper complement those of our previous study on neutron hole Pb isotopes, confirming that realistic effective interactions are now able to reproduce with quantitative accuracy the spectroscopic properties of complex nuclei.

nucl-th↗

arXiv1998

Realistic Shell-Model Calculations for 208Pb Neighbors

We have performed a shell-model study of the two nuclei 210Po and 206Hg, having and lacking two protons with respect to doubly magic 208Pb. In our calculations we have employed realistic effective interactions derived from the Bonn A nucleon-nucleon potential. The calculated results are compared with the available experimental data are, however, very scanty for 206Hg. The very good agreement obtained for 210Po supports confidence in our predictions for 206Hg.

nucl-th↗

arXiv1998

Neutron-Proton Interaction in Doubly Odd Deformed Nuclei

In this paper, we present some results of a particle-rotor model study of 176Lu. In particular, we consider the two lowest K=1+ balds, which present a rather large odd-even staggering. This effect, which may be traced to direct Coriolis coupling with Newby-shifted K=0+ bands, is of great interest since it gives information on the proton-neutron interaction. We use both zero-range and finite-range interactions with particular attention focused on the role of the tensor force. Comparison of the calculated results with experimental data evidences the importance of the tensor-force effects in the description of the odd-even staggering in K not-equal-to zero bands.

nucl-th↗

arXiv1998

Realistic Effective Intaractions and Nuclear Structure Calculations

We address the two main questions relevant to microscopic nuclear structure calculations starting from a free NN potential. These concern the accuracy of these kinds of calculations and the extent to which they depend on the potential used as input. Regarding the first question, we present some results obtained for nuclei around doubly magic 132Sn and 208Pb by making use of an effective interaction derived from the Bonn A potential. Comparison shows that our results are in very good agreement with the experimental data. As for the second question, we present the results obtained for the nucleus 134Te by making use of four different NN potentials. They indicate that nuclear structure calculations may help in understanding the off-shell nature of the NN potential.

nucl-th↗

arXiv1998

Bonn Potential and Shell-Model Calculations for 206,205,204Pb

The structure of the nuclei 206,205,204Pb is studied interms of shell model employing a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The energy spectra, binding energies and electromagnetic properties are calculated and compared with experiment. A very good overall agreement is obtained. This evidences the reliability of our realistic effective interaction and encourages use of modern realistic potentials in shell-model calculations for heavy-mass nuclei.

nucl-th↗

arXiv1998

Realistic Shell-Model Calculations for Nuclei in the Region of Shell Closures off Stability

We have performed realistic shell-model calculations for nuclei around doubly magic 100Sn and 132Sn using an effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in remarkably good agreement with the experimental data showing the ability of our effective interaction to provide an accurate description of nuclear structure properties.

nucl-th↗

arXiv1998

Proton Particle-Neutron Hole States in 132Sb with a Realistic Interaction

The structure of the particle-hole nucleus 132Sb provides a direct source of information on the effective neutron-proton interaction in the 132Sn region. We have performed a shell-model calculation for this nucleus using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in very good agreement with the experimental data evidencing the reliability of our effective interaction matrix elements both with isospin T=1 and T=0.

nucl-th↗