M. Waroquier

Fragmentation of single-particle strength in spherical open-shell nuclei: Application to the spectral functions in 142Nd

V. Van der Sluys, D. Van Neck, M. Waroquier, J. Ryckebusch
Nuclear Physics A
551 (2), 210-240
1993
A1
Published while none of the authors were employed at the CMM

Abstract 

A method is presented for the calculation of single-particle strength distributions in spherical semi-magic open-shell nuclei. The model is based upon the equation-of-motion method and differs from the standard quasiparticle-phonon model in that also backward-going terms are included in the self-energy of the nucleons. In the limit to closed shells the model reduces to the microscopic particle-vibration method with RPA-like polarization propagators. The model is applied to the proton particle and hole spectral functions in the odd nuclei adjacent to 142Nd.

Do proton-neutron pairs behave like quasideuterons in the photoabsorption process?

J. Ryckebusch, L. Machenil, M. Vanderhaeghen, M. Waroquier
Physics Letters B
291 (3), 213-217
1992
A1
Published while none of the authors were employed at the CMM

Abstract 

Calculations have been performed for the 16O(γ,pn) reaction in the photon-energy range Eγ=50–300MeV. Effects due to both one-pion exchange currents and the Δ have been included. We discriminate between different couplings of the initial proton-neutron (pn) pair involved in the reaction. At lower photon energies where the pion exchange currents dominate the cross section it is found that pn pairs in the finite nucleus do not fully behave like a quasideuteron. Therefore, we feel that the factorized form of the (γ,pn) cross section should be used with reservation.

Occupation numbers in a shell-model approach

D. Van Neck, M. Waroquier, V. Van der Sluys, J. Ryckebusch
Physics Letters B
274 (2), 143-148
1992
A1
Published while none of the authors were employed at the CMM

Abstract 

It is reminded that a shell-model approach for occupation numbers in nuclei imposes constraints on the number of particles that can be lifted out of the Fermi sea. These constraints do not depend on the details of the calculation, such as the applied effective interaction, the size of the shell-model space or the way of tackling the shell-model equations. In some recent papers these constraints are violated. It is shown that this points to inconsistencies in the normalization of the many-body wave function calculated within perturbation theory.

Self-consistent solution of the second-order Dyson equation for single-particle propagators, with application to the spectral functions of 48Ca

D. Van Neck, M. Waroquier, J. Ryckebusch
Nuclear Physics A
530 (2), 347-369
1991
A1
Published while none of the authors were employed at the CMM

Abstract 

We present a new method to describe the fragmentation of single-particle strength in the framework of the Green function formalism. By means of an iterative scheme, we are able to construct a self-consistent solution of the Dyson equation up to second order in the interaction. Damping effects, such as the broadening of the spectral function for deep-lying hole states, show up in a natural way. We apply the formalism to a schematic model and to the case of the doubly-closed shell nucleus 48Ca.

Coincidence 58Ni(e, e′pi) cross sections at moderate energy and momentum transfer

J. Ryckebusch, K. Heyde, D. Van Neck, M. Waroquier
Nuclear Physics A
505 (3-4), 755-778
1989
A1
Published while none of the authors were employed at the CMM

Abstract 

We present results of self-consistent Hartree-Fock (HF) and continuum random-phase-approximation (RPA) calculations for proton emission following the electro-excitation of 58Ni in the energy range ω = 25–42 MeV. The calculations are performed for four different values of the momentum transfer ranging between 0.4 and 0.8 fm−1. For the above kinematics, an extensive amount of data is available. We confront the data with the theoretical results obtained within the plane-wave impulse approximation (PWIA), HF and RPA. The role of the final-state interaction (FSI) is investigated. Furthermore, we investigate in how far the angular distributions may reflect the occurrence of giant resonances. A quasi-free knockout (QFK) reaction picture is found unable to account for details of the data. Although the RPA offers a reasonable description of the overall q and ω behaviour of the angular distributions, it does not provide a good description of the proton-decay branch of the quadrupole and octupole resonance.

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