Pygmy and core polarization dipole modes in 206 Pb: Connecting nuclear structure to stellar nucleosynthesis

Published

Journal Article

© 2017 A high-resolution study of the electromagnetic response of 206Pb below the neutron separation energy is performed using a γ→,γ′) experiment at the HIγ→S facility. Nuclear resonance fluorescence with 100% linearly polarized photon beams is used to measure spins, parities, branching ratios, and decay widths of excited states in 206Pb from 4.9 to 8.1 MeV. The extracted ΣB(E1)↑ and ΣB(M1)↑ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9±0.2 e2fm2 and 8.3±2.0μN2, respectively. These measurements are found to be in very good agreement with the predictions from an energy-density functional (EDF) plus quasiparticle phonon model (QPM). Such a detailed theoretical analysis allows to separate the pygmy dipole resonance from both the tail of the giant dipole resonance and multi-phonon excitations. Combined with earlier photonuclear experiments above the neutron separation energy, one extracts a value for the electric dipole polarizability of 206Pb of αD=122±10 mb/MeV. When compared to predictions from both the EDF+QPM and accurately calibrated relativistic EDFs, one deduces a range for the neutron-skin thickness of Rskin206=0.12–0.19 fm and a corresponding range for the slope of the symmetry energy of L=48–60 MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section Pb205(n,γ)Pb206 at 30 keV to be σ=130±25 mb. The astrophysical impact of this measurement—on both the s-process in stellar nucleosynthesis and on the equation of state of neutron-rich matter—is discussed.

Full Text

Duke Authors

Cited Authors

  • Tonchev, AP; Tsoneva, N; Bhatia, C; Arnold, CW; Goriely, S; Hammond, SL; Kelley, JH; Kwan, E; Lenske, H; Piekarewicz, J; Raut, R; Rusev, G; Shizuma, T; Tornow, W

Published Date

  • October 10, 2017

Published In

Volume / Issue

  • 773 /

Start / End Page

  • 20 - 25

International Standard Serial Number (ISSN)

  • 0370-2693

Digital Object Identifier (DOI)

  • 10.1016/j.physletb.2017.07.062

Citation Source

  • Scopus