Low-energy electric dipole response of Sn isotopes

Abstract

We study the low-energy dipole (LED) strength distribution along the Sn isotopic chain in both the isoscalar (IS) and the isovector (IV, or E1) electric channels, to provide testable predictions and guidance for new experiments with stable targets and radioactive beams. We use the self-consistent Quasi-particle Random-Phase Approximation (QRPA) with finite-range interactions and mainly the Gogny D1S force. We analyze also the performance of a realistic two-body interaction supplemented by a phenomenological three-body contact term. We find that from N=50 and up to the N=82 shell closure (132Sn) the lowest-energy part of the IS-LED spectrum is dominated by a collective transition whose properties vary smoothly with neutron number and which cannot be interpreted as a neutron-skin oscillation. For the neutron-rich species this state contributes to the E1 strength below particle threshold, but much more E1 strength is carried by other, weak but numerous transitions around or above threshold. We find that strong structural changes in the spectrum take effect beyond N=82, namely increased LED strength and lower excitation energies. Our results with the Gogny interaction are compatible with existing data. On this basis we predict that a) the summed IS strength below particle threshold shall be of the same order of magnitude for N=50-82, b) the summed E1 strength up to approximately 12 MeV shall be similar for N=50-82 MeV, while c) the summed E1 strength below threshold shall be of the same order of magnitude for N ~ 64 - 82 and much weaker for the lighter, more-symmetric isotopes. We point out a general agreement of our results with other non-relativistic studies, the absence of a collective IS mode in some of those studies, and a possibly radical disagreement with relativistic models.

v2: 13 pages, incl. 10 figures; extended discussion, esp. of collectivity; revised Fig.9; to appear in Phys.Rev.C

References in corpus (18)

• Exotic modes of excitation in atomic nuclei far from stability
• Pygmy dipole resonance as a constraint on the neutron skin of heavy nuclei
• Investigation of Pygmy Dipole Resonances in the Tin Region
• Isospin Character of the Pygmy Dipole Resonance in 124Sn
• Pygmy Resonances and Neutron Skins
• Large-scale Continuum Random Phase Approximation predictions of dipole strength for astrophysical applications
• Self-consistent description of multipole strength: systematic calculations
• Proton elastic scattering from tin isotopes at 295 MeV and systematic change of neutron density distributions
• Information content of the low-energy electric dipole strength: correlation analysis
• Self-consistent calculations of the strength function and radiative neutron capture cross section for stable and unstable tin isotopes
• Relativistic two-phonon model for low-energy nuclear response
• Quasiparticle Random Phase Approximation with Interactions from the Similarity Renormalization Group
• Isoscalar dipole coherence at low energies and forbidden E1 strength
• Pairing in the Framework of the Unitary Correlation Operator Method (UCOM): Hartree-Fock-Bogoliubov Calculations
• Pygmy and giant electric dipole responses of medium-heavy nuclei in a self-consistent Random Phase Approximation approach with finite-range interaction
• Skyrme-Hartree-Fock Description of the Dipole Strength in Neutron-Rich Tin Isotopes
• Toroidal, compression, and vortical dipole strengths in 124Sn
• Systematic investigation of E1 strength for the isotopes from Z = 28 to 50

Cited by in corpus (20)

• Low-energy electric dipole response in 120Sn
• Low-energy dipole strength in 112,120Sn
• Electric and magnetic dipole modes in high-resolution inelastic proton scattering at $0^{\circ }$
• Electric and magnetic dipole strength in 112,114,116,118,120,124Sn
• Dipole response in 208Pb within a self-consistent multiphonon approach
• Evolution of the dipole polarizability in the stable tin isotope chain
• Interplay between low-lying isoscalar and isovector dipole modes: a comparative analysis between semi-classical and quantum approaches
• Isoscalar and neutron modes in the E1 spectra of Ni isotopes and the relevance of shell effects and the continuum
• Indirect methods in nuclear astrophysics with relativistic radioactive beams
• The decay of quadrupole-octupole $1^{-}$ states in ${}^{40}$Ca and ${}^{140}$Ce
• Excitation spectra of exotic nuclei in a self-consistent phonon-coupling model
• Systematics of the low-energy electric dipole strength in the Sn isotopic chain
• Low-lying electric-dipole strengths of Ca, Ni, and Sn isotopes imprinted on total reaction cross sections
• Nuclear breathing mode in neutron-rich Nickel isotopes: sensitivity to the symmetry energy and the role of the continuum
• Nuclear collective dynamics within Vlasov approach
• Emergence of low-energy monopole strength in the neutron-rich calcium isotopes
• Dynamical Coupling of Pygmy and Giant Resonances in Relativistic Coulomb Excitation
• Giant Resonances based on Unitarily Transformed Two-Nucleon plus Phenomenological Three-Nucleon Interactions
• Proton pygmy resonances: predictions for N=20 isotones
• Pigmy resonances, transfer, and separable potentials