Pygmy and core polarization dipole modes in 206Pb: 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

Physics Letters B (Oct 2017)

Pygmy and core polarization dipole modes in 206Pb: 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

Affiliations

A.P. Tonchev: Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA; Duke University, Department of Physics, Box 90308, Durham, NC 27708-0308, USA; Corresponding author at: Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
N. Tsoneva: Institut für Theoretische Physik, Universität Gießen, Heinrich-Buff-Ring 16, D-35392 Gießen, Germany
C. Bhatia: Society for Applied Microwave Electronics Engineering and Research, Indian Institute of Technology, Mumbai Campus, India; Duke University, Department of Physics, Box 90308, Durham, NC 27708-0308, USA; Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308, USA
C.W. Arnold: Bettis Atomic Power Laboratory, West Mifflin, PA 15122, USA; Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
S. Goriely: Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, Campus de la Plaine, CP-226, 1050 Brussels, Belgium
S.L. Hammond: Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA; Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308, USA
J.H. Kelley: Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA; Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308, USA
E. Kwan: National Superconducting Cyclotron Laboratory, East Lansing, MI 48824, USA
H. Lenske: Institut für Theoretische Physik, Universität Gießen, Heinrich-Buff-Ring 16, D-35392 Gießen, Germany
J. Piekarewicz: Department of Physics, Florida State University, Tallahassee, FL 32306-4350, USA
R. Raut: UGC-DAE Consortium for Scientific Research, Kolkata Centre LB-8 Sector-III, Bidhannagar, Kolkata 700098, India
G. Rusev: Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
T. Shizuma: Quantum Beam Science Center, Japan Atomic Energy Agency, Tokai-mura, Ibaraki 319-1184, Japan
W. Tornow: Duke University, Department of Physics, Box 90308, Durham, NC 27708-0308, USA; Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308, USA

Journal volume & issue: Vol. 773
pp. 20 – 25

Abstract

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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. Keywords: 206Pb, Pygmy dipole resonance, Giant dipole resonance, Skin thickness and dipole polarizability, Pb205(n,γ)Pb206 reaction cross section

Published in Physics Letters B

ISSN: 0370-2693 (Print); 1873-2445 (Online)
Publisher: Elsevier
Country of publisher: Netherlands
LCC subjects: Science: Physics
Website: http://www.journals.elsevier.com/physics-letters-b/

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