Pygmy dipole resonances as a manifestation of the structure of the neutron-rich nuclei

Tsoneva, N.; Lenske, H.; Stoyanov, Chavdar

doi:10.1016/s0375-9474\(04\)90029-2

Cited by 9 publications

(23 citation statements)

References 18 publications

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“…Moreover, below 8 MeV in the most of the examined nuclei we observe that the quasiparticle-phonon coupling is the only mechanism which brings the strength to this region where the pure RQRPA has no solutions at all. We have found also general agreement of our results for 116,130 Sn and 88 Sr with the relatively recent studies of the low-lying dipole strength in Refs [67,68]. in the Quasiparticle Phonon…”

supporting

confidence: 92%

Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei

2008

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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-quasiparticle 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) 88 Sr, 90 Zr, 92 Mo is performed within this framework.

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confidence: 92%

Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei

2008

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“…The second point we would like to discuss is related to the fact that our calculations do not consider effects beyond one-particle one-hole (1p-1h) excitations, even though in the literature there are now quite a few calculations of the PDR excitations where these effects are taken into account [1][2][3][16][17][18][19][20]. The inclusion of p-h excitations beyond those considered by the RPA produces two effects related to the real and imaginary part of the self-energy.…”

Section: The Modelmentioning

confidence: 99%

“…Non relativistic [5][6][7] and relativistic [8][9][10] RPA approaches have been used in the past to investigate the PDR. Studies of PDR have been also done with more elaborated nuclear models containing pairing [11][12][13][14] and spreading widths [15][16][17][18][19][20][21]. Usually these calculations have been done to make detailed investigations of the PDR characteristics in a limited set of isotopes.…”

Section: Introductionmentioning

confidence: 99%

Evolution of the pygmy dipole resonance in nuclei with neutron excess

et al. 2009

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The electric dipole excitation of various nuclei is calculated with a Random Phase Approximation phenomenological approach. The evolution of the strength distribution in various groups of isotopes, oxygen, calcium, zirconium and tin, is studied. The neutron excess produces $E1$ strength in the low energy region. Indexes to measure the collectivity of the excitation are defined. We studied the behavior of proton and neutron transition densities to determine the isoscalar or isovector nature of the excitation. We observed that in medium-heavy nuclei the low-energy $E1$ excitation has characteristics rather different that those exhibited by the giant dipole resonance. This new type of excitation can be identified as pygmy dipole resonance.Comment: 14 pages, 12 figures, 7 table

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“…If combined with results on the stable isotopes, for the first time a set of data spanning a large range of N/Z ratios from about 1.25 to 1.68 would be available, which can serve as a benchmark test for the validity of various theoretical approaches. Indeed, the Sn isotopes have been a favorite case in the model calculations studying features of the PDR as a function of neutron excess [2,4,16,19,[47][48][49][50][51][52][53][54][55][56][57][58][59].…”

Section: Introductionmentioning

confidence: 99%

Low-energy dipole strength inSn112,120

et al. 2014

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The 112,120 Sn(γ, γ ) reactions below the neutron separation energies have been studied at the superconducting Darmstadt electron linear accelerator S-DALINAC for different endpoint energies of the incident bremsstrahlung spectrum. Dipole strength distributions are extracted for 112 Sn up to 9.5 MeV and for 120 Sn up to 9.1 MeV. A concentration of dipole excitations is observed between 5 and 8 MeV in both nuclei. Missing strength due to unobserved decays to excited states is estimated in a statistical model. A fluctuation analysis is applied to the photon scattering spectra to extract the amount of the unresolved strength hidden in background due to fragmentation. The strength distributions are discussed within different model approaches such as the quasiparticle-phonon model and the relativistic time blocking approximation allowing for an inclusion of complex configurations beyond the initial particle-hole states. While a satisfactory description of the fragmentation can be achieved for sufficently large model spaces, the predicted centroids and total electric dipole strengths for stable tin isotopes strongly depend on the assumptions about the underlying mean field.

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Pygmy dipole resonances as a manifestation of the structure of the neutron-rich nuclei

Cited by 9 publications

References 18 publications

Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei

Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei

Evolution of the pygmy dipole resonance in nuclei with neutron excess

Low-energy dipole strength inSn112,120

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