arXiv subjects

T. Engeland

Publications and source records attributed to T. Engeland.

15 recordsLinked to original sources

arXiv2006

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.

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arXiv2005

Dominant g(9/2)^2 neutron configuration in the 4+1 state of 68Zn based on new g factor measurements

The $g$ factor of the $4_1^+$ state in $^{68}$Zn has been remeasured with improved energy resolution of the detectors used. The value obtained is consistent with the previous result of a negative $g$ factor thus confirming the dominant $0g_{9/2}$ neutron nature of the $4_1^+$ state. In addition, the accuracy of the $g$ factors of the $2_1^+$, $2_2^+$ and $3_1^-$ states has been improved an d their lifetimes were well reproduced. New large-scale shell model calculations based on a $^{56}$Ni core and an $0f_{5/2}1pg_{9/2}$ model space yield a theoretical value, $g(4_1^+) = +0.008$. Although the calculated value is small, it cannot fully explain the experimental value, $g(4_1^+) = -0.37(17)$. The magnitude of the deduced B(E2) of the $4_1^+$ and $2_1^+$ transition is, however, rather well described. These results demonstrate again the importance of $g$ factor measurements for nuclear structure determination s due to their specific sensitivity to detailed proton and neutron components in the nuclear wave functions.

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arXiv2004

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.

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arXiv2004

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.

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arXiv2000

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.

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arXiv2000

Application of realistic effective interactions to the structure of the Zr isotopes

We calculate the low-lying spectra of the zirconium isotopes Z=40 with neutron numbers from N=52 to N=60 using the 1p1/20g9/2 proton and 2s1d0g7/20h11/2 neutron sub-shells to define the model space. Effective proton-proton, neutron--neutron and proton-neutron interactions have been derived using 88Sr as closed core and employing perturbative many-body techniques. The starting point is the nucleon-nucleon potential derived from modern meson exchange models. The comprehensive shell-model calculation performed in this work provides a qualitative reproduction of essential properties such as the sub-shell closures in 96Zr and 98Zr.

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arXiv1999

Pairing correlations in nuclear systems, from infinite matter to finite nuclei

Finite nuclei such as those found in the chain of even tin isotopes from ^{102}Sn to ^{130}Sn, exhibit a near constancy of the 2^+_1-0^+_1 excitation energy, a constancy which can be related to strong pairing correlations and the near degeneracy in energy of the relevant single particle orbits. Large shell-model calculations for these isotopes reveal that the major contribution to pairing correlations in the tin isotopes stems from the ^1S_0 partial wave in the nucleon-nucleon interaction. Omitting this partial wave and the ^3P_2 wave in the construction of an effective interaction, results in a spectrum which has essentially no correspondence with experiment. These partial wave are also of importance for infinite neutron matter and nuclear matter and give the largest contribution to the pairing interaction and energy gap in neutron star matter.

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arXiv1999

Shell model studies of the proton drip line nucleus $^{106}$Sb

We present results of shell model calculations for the proton drip line nucleus $^{106}$Sb. The shell model calculations were performed based on an effective interaction for the $2s1d0g_{7/2}0h11_{11/2}$ shells employing modern models for the nucleon-nucleon interaction. The results are compared with the recently proposed experimental yrast states. A good agreement with experiment is found lending support to the experimental spin assignements.

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arXiv1998

Realistic Effective Interactions and Large-Scale Nuclear Structure Calculation

We describe the properties of complex nuclei, such as the Sn isotopes with mass numbers A = 100 - 132, in terms of the free nucleon--nucleon interaction as obtained from meson--exchange theory. This amounts to first calculating an effective interaction in which the free interaction is modified by the presence of the appropriate nuclear medium. The short--range correlations are included within the framework of Brueckner theory yielding the nuclear reaction matrix and the long--range correlations by using the reaction matrix in many--body perturbation theory to obtain an effective interaction. The resulting effective interaction is then employed in calculating the nuclear properties. Particular emphasis is placed on the ability of our calculation to describe systematic trends of the properties of these nuclei. Both successful achievements and problematic features are pointed out.

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arXiv1997

Study of odd-mass N=82 isotones with realistic effective interactions

The microscopic quasiparticle-phonon model, MQPM, is used to study the energy spectra of the odd $Z=53 - 63$, N=82 isotones. The results are compared with experimental data, with the extreme quasiparticle-phonon limit and with the results of an unrestricted $2s1d0g_{7/2}0h_{11/2}$ shell model (SM) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the $\hat{Q}$-box method whereas for the MQPM the effective interaction is defined by the G-matrix.

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arXiv1997

Effective interactions and shell model studies of heavy tin isotopes

We calculate the low-lying spectra of heavy tin isotopes from A=120 to A=130 using the 2s1d0g_{7/2}0h_{11/2} shell to define the model space. An effective interaction has been derived using 132Sn as closed core employing perturbative many-body techniques. We start from a nucleon-nucleon potential derived from modern meson exchange models. This potential is in turn renormalized for the given medium, 132Sn, yielding the nuclear reaction matrix, which is then used in perturbation theory to obtain the shell model effective interaction.

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arXiv1996

Extended shell-model calculation for even N=82 isotones with realistic effective interactions

The shell model within the $2s1d0g_{7/2}0h_{11/2}$ shell is applied to calculate nuclear structure properties of the even Z=52 - 62, N=82 isotones. The results are compared with experimental data and with the results of a quasiparticle random-phase approximation (QRPA) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the $\hat{Q}$-box method whereas for the QRPA the effective interaction is defined by the G-matrix.

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arXiv1996

Generalized seniority scheme in light Sn isotopes

The yrast generalized seniority states are compared with the corresponding shell model states for the case of the Sn isotopes $^{104-112}$Sn. For most of the cases the energies agree within 100 keV and the overlaps of the wave functions are greater than 0.7.

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arXiv1994

Comment on "No-core calculations" of the spectra of light nuclei

We comment upon a recent work by Zheng, Barrett, Jaqua, Vary and McCarthy, concerning calculations of spectra of light nuclei with no core. It is demonstrated that the omission of particle-particle ladder diagrams in their calculations, explains the large differences between results obtained with various model spaces.

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arXiv1993

The structure of the neutron deficient Sn isotopes

We calculate the spectra for the neutron deficient Sn isotopes with mass numbers from A=102 to A=108, using standard many-body techniques. The G-matrix used in the perturbative expansion was calculated using the Bonn potentials. A good agreement with the available data is obtained.

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