307 research outputs found
Effective interactions and the nuclear shell-model
This review aims at a critical discussion of the interplay between effective
interactions derived from various many-body approaches and spectroscopic data
extracted from large scale shell-model studies. To achieve this, our many-body
scheme starts with the free nucleon-nucleon (NN) interaction, typically
modelled on various meson exchanges. The NN interaction is in turn renormalized
in order to derive an effective medium dependent interaction. The latter is in
turn used in shell-model calculations of selected nuclei. We also describe how
to sum up the parquet class of diagrams and present initial uses of the
effective interactions in coupled cluster many-body theory.Comment: 61 pages, submitted to Prog. Part. Nucl. Phy
Effective interactions and shell model studies of heavy tin isotopes
We present results from large-scale shell-model calculations of even and odd
tin isotopes from 134Sn to 142}Sn with a shell-model space defined by the
1f7/2,2p3/2,0h9/2,2p1/2,1f5/2,0i13/2 single-particle orbits. An effective
two-body interaction based on modern nucleon-nucleon interactions is employed.
The shell-model results are in turn analyzed for their pairing content using a
generalized seniority approach. Our results indicate that a pairing-model
picture captures a great deal of the structure and the correlations of the
lowest lying states for even and odd isotopes.Comment: 7 pages, revtex latex style, submitted to PR
Effective interactions in medium heavy nuclei
We present a brief overview of microscopic nuclear structure approaches to
nuclei with mass number from 100 to 132. The emphasis is on the shell model and
theories for deriving effective interactions starting from the free
interactions between nucleons. New results for (105,106,107)Sb are presented.Comment: Proceedings of RNB5, 3-8 April 2000, Divonne, France. 6 pages,
Elsevier latex style. To appear in Nucl. Phys.
Model Calculation of Effective Three-Body Forces
We propose a scheme for extracting an effective three-body interaction
originating from a two-nucleon interaction. This is based on the Q-box method
of Kuo and collaborators, where folded diagrams are obtained by differentiating
a sum of non-folded diagrams with respect to the starting energy. To gain
insight we have studied several examples using the Lipkin model where the
perturbative approach can be compared with exact results. Numerically the
three-body interactions can be significant and in a matrix example good
accuracy was not obtained simultaneously for both eigenvalues with two-body
interactions alone.Comment: 9 pages, Revtex4, 7 figs, submitted to PR
Comparison of the Effective Interaction to Various Orders in Different Mass Regions
The convergence of the perturbation expansion for the effective interaction
to be used in shell-model calculations is investigated as function of the mass
number , from to . As the mass number increases, there are more
intermediate states to sum over in each higher-order diagram which contributes
to the effective interaction. Together with the fact that the energy
denominators in each diagram are smaller for larger mass numbers, these two
effects could largely enhance higher-order contributions to the effective
interaction, thereby deteriorating the order-by-order convergence of the
effective interaction. This effect is counterbalanced by the short range of the
nucleon-nucleon interaction, which implies that its matrix elements are weaker
for valence single-particle states in ``large'' nuclei with large mass number
as compared to those in light nuclei. These effects are examined by comparing
various mean values of the matrix elements. It turns out that the contributions
from higher-order terms remain fairly stable as the mass number increases from
to . The implications for nuclear structure calculations are
discussed.Comment: Revtex, 20 pages, 1 figure not include
Convergence properties of the effective interaction
The convergence properties of two perturbative schemes to sum the so-called
folded diagrams are critically reviewed, with an emphasis on the intruder state
problem. The methods we study are the approaches of Kuo and co-workers and Lee
and Suzuki. The suitability of the two schemes for shell-model calculations are
discussed.Comment: 10 pages in revtex ver. 3.0. 3 figs can be obtained upon request.
Univerisity of Oslo report UiO/PHYS/93-2
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