[Submitted on 11 Aug 2017] (cross-list from nucl-ex)
Pygmy and core polarization dipole modes in Pb: connecting nuclear structure to stellar nucleosynthesis
A.P. Tonchev🇺🇸 · N. Tsoneva🇩🇪 · C. Bhatia🇮🇳 · C.W. Arnold🇺🇸 · S. Goriely🇧🇪 · S.L. Hammond🇺🇸 · J.H. Kelley🇺🇸 · E. Kwan🇺🇸 · H. Lenske🇩🇪 · J. Piekarewicz🇺🇸 · R. Raut🇮🇳 · G. Rusev🇺🇸 · T. Shizuma🇯🇵 · W. Tornow🇺🇸
A high-resolution study of the electromagnetic response of Pb below the neutron separation energy is performed using a (,) experiment at the HIS 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 Pb from to MeV. The extracted (E1) and (M1) values for the total electric and magnetic dipole strength below the neutron separation energy are 0.90.2efm and 8.32.0, 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 Pb of 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 -fm and a corresponding range for the slope of the symmetry energy of -MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section Pb(n,)Pb at 30keV to be 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.
- Comments:
- 8 pages and 4 figures. Manuscript accepted for publication in Physics Letters B
- Subjects:
- Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
- arXiv:
- 1708.03522 [pdf]