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Title: Quasiparticle time blocking approximation in coordinate space as a model for the damping of the giant dipole resonance

Abstract

The quasiparticle time blocking approximation (QTBA) is presented as a model for the description of natural-parity excitations in open-shell nuclei. Most attention is paid to the question of the damping of the giant dipole resonance. Within the model pairing correlations, two-quasiparticle (2q), and 2qxphonon configurations are included. Thus the QTBA is an extension of the quasiparticle random phase approximation to include quasiparticle-phonon coupling. Calculational formulas are presented for the case of neutral natural-parity excitations in spherical nuclei. The main equations are written in the coordinate representation that allows to take into account single-particle continuum completely. The QTBA is applied to describe E1 photoabsorption cross sections in nuclei {sup 116,120,124}Sn. It has been obtained that the 2q(multiply-in-circle sign)phonon configurations provide noticeable fragmentation of the giant dipole resonance resulting in the appearance of a significant spreading width. The results are compared with available experimental data.

Authors:
 [1];  [2];  [3]
  1. Institute of Physics and Power Engineering, RU-249033 Obninsk (Russian Federation)
  2. (Germany)
  3. Nuclear Physics Department, V. A. Fock Institute of Physics, St. Petersburg State University, RU-198504 St. Petersburg (Russian Federation)
Publication Date:
OSTI Identifier:
20995280
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevC.75.054318; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CHANNELING; CROSS SECTIONS; DIPOLES; EXCITATION; PARITY; PHONONS; RANDOM PHASE APPROXIMATION; RESONANCE; SPHERICAL CONFIGURATION; TIN 116; TIN 120; TIN 124

Citation Formats

Litvinova, E. V., Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching, and Tselyaev, V. I. Quasiparticle time blocking approximation in coordinate space as a model for the damping of the giant dipole resonance. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.054318.
Litvinova, E. V., Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching, & Tselyaev, V. I. Quasiparticle time blocking approximation in coordinate space as a model for the damping of the giant dipole resonance. United States. doi:10.1103/PHYSREVC.75.054318.
Litvinova, E. V., Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching, and Tselyaev, V. I. Tue . "Quasiparticle time blocking approximation in coordinate space as a model for the damping of the giant dipole resonance". United States. doi:10.1103/PHYSREVC.75.054318.
@article{osti_20995280,
title = {Quasiparticle time blocking approximation in coordinate space as a model for the damping of the giant dipole resonance},
author = {Litvinova, E. V. and Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching and Tselyaev, V. I.},
abstractNote = {The quasiparticle time blocking approximation (QTBA) is presented as a model for the description of natural-parity excitations in open-shell nuclei. Most attention is paid to the question of the damping of the giant dipole resonance. Within the model pairing correlations, two-quasiparticle (2q), and 2qxphonon configurations are included. Thus the QTBA is an extension of the quasiparticle random phase approximation to include quasiparticle-phonon coupling. Calculational formulas are presented for the case of neutral natural-parity excitations in spherical nuclei. The main equations are written in the coordinate representation that allows to take into account single-particle continuum completely. The QTBA is applied to describe E1 photoabsorption cross sections in nuclei {sup 116,120,124}Sn. It has been obtained that the 2q(multiply-in-circle sign)phonon configurations provide noticeable fragmentation of the giant dipole resonance resulting in the appearance of a significant spreading width. The results are compared with available experimental data.},
doi = {10.1103/PHYSREVC.75.054318},
journal = {Physical Review. C, Nuclear Physics},
number = 5,
volume = 75,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Theoretical studies of low-lying dipole strength in even-even spherical nuclei within the relativistic quasiparticle time blocking approximation (RQTBA) are presented. The RQTBA developed recently as an extension of the self-consistent relativistic quasiparticle random-phase approximation (RQRPA) enables one to investigate the effects of the coupling of two-quasiparticle excitations to collective vibrations within a fully consistent calculation scheme based on covariant energy density functional theory. Dipole spectra of even-even {sup 130}Sn-{sup 140}Sn and {sup 68}Ni-{sup 78}Ni isotopes calculated within both RQRPA and RQTBA show two well-separated collective structures: the higher lying giant dipole resonance and the lower lying pygmy dipole resonance, whichmore » can be identified by the different behavior of the transition densities of states in these regions.« less
  • The self-consistent relativistic quasiparticle random-phase approximation (RQRPA) is extended by the quasiparticle-phonon coupling (QPC) model using the quasiparticle time blocking approximation (QTBA). The method is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticle space with an energy-dependent two-quasiparticle residual interaction. This equation is solved either in the basis of Dirac states forming the self-consistent solution of the ground state or in the momentum representation. Pairing correlations are treated within the Bardeen-Cooper-Schrieffer (BCS) model with a monopole-monopole interaction. The same NL3 set of the coupling constants generates the Dirac-Hartree-BCS single-quasiparticle spectrum, the static part of the residual two-quasiparticlemore » interaction and the quasiparticle-phonon coupling amplitudes. A quantitative description of electric dipole excitations in the chain of tin isotopes (Z=50) with the mass numbers A=100,106,114,116,120, and 130 and in the chain of isotones with (N=50) {sup 88}Sr, {sup 90}Zr, {sup 92}Mo is performed within this framework. The RQRPA extended by the coupling to collective vibrations generates spectra with a multitude of 2q x phonon (two quasiparticles plus phonon) states providing a noticeable fragmentation of the giant dipole resonance as well as of the soft dipole mode (pygmy resonance) in the nuclei under investigation. The results obtained for the photo absorption cross sections and for the integrated contributions of the low-lying strength to the calculated dipole spectra agree very well with the available experimental data.« less
  • No abstract prepared.
  • The problem of the microscopic description of excited states of the even-even open-shell atomic nuclei is considered. A model is formulated which allows one to go beyond the quasiparticle random phase approximation. The physical content of the model is determined by the quasiparticle time blocking approximation (QTBA) which enables one to include contributions of the two-quasiparticle and the two-phonon configurations, while excluding (blocking) more complicated intermediate states. In addition, the QTBA ensures consistent treatment of ground state correlations in the Fermi systems with pairing. The model is based on the generalized Green function formalism (GGFF) in which the normal andmore » the anomalous Green functions are treated in a unified way in terms of the components of generalized Green functions in a space that is double the size of the usual single-particle space. Modification of the GGFF is considered in the case when the many-body nuclear Hamiltonian contains two-, three-, and other many-particle effective forces.« less