skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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±0.2e 2fm 2 and 8.3±2.0μ$$2\atop{N}$$, 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 α D=122±10mb/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 R$$206\atop{skin}$$=0.12–0.19fm and a corresponding range for the slope of the symmetry energy of L=48–60MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section 205Pb(n,γ)Pb 206 at 30 keV to be σ=130±25mb. In conclusion, 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.

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [6];  [7];  [2];  [8];  [9];  [10];  [11];  [12]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Duke Univ., Durham, NC (United States)
  2. Univ. GieBen, GieBen (Germany)
  3. Indian Institute of Technology, (India); Duke Univ., Durham, NC (United States); Triangle Univ. Nuclear Lab., Durham, NC (United States)
  4. Bettis Atomic Power Lab., West Mifflin, PA (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  5. Univ. Libre de Bruxelles, Brussels (Belgium)
  6. Univ. of North Carolina, Chapel Hill, NC (United States); Triangle Univ. Nuclear Lab., Durham, NC (United States)
  7. National Superconducting Cyclotron Lab., East Lansing, MI (United States)
  8. Florida State Univ., Tallahassee, FL (United States)
  9. UGC-DAE Consortium for Scientific Research, Kolkata (India)
  10. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  11. Japan Atomic Energy Agency, Ibaraki (Japan)
  12. Duke Univ., Durham, NC (United States); Triangle Univ. Nuclear Lab., Durham, NC (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1373624
Report Number(s):
LLNL-JRNL-716577
Journal ID: ISSN 0370-2693
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Published Article
Journal Name:
Physics Letters. Section B
Additional Journal Information:
Journal Volume: 773; Journal Issue: C; Journal ID: ISSN 0370-2693
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 79 ASTRONOMY AND ASTROPHYSICS; 206Pb; Pygmy dipole resonance; Giant dipole resonance; Skin thickness and dipole polarizability; Pb205(n,γ)Pb206; reaction cross section

Citation Formats

Tonchev, A. P., Tsoneva, N., Bhatia, C., Arnold, C. W., Goriely, S., Hammond, S. L., Kelley, J. H., Kwan, E., Lenske, H., Piekarewicz, J., Raut, R., Rusev, G., Shizuma, T., and Tornow, W.. Pygmy and core polarization dipole modes in 206Pb: Connecting nuclear structure to stellar nucleosynthesis. United States: N. p., 2017. Web. doi:10.1016/j.physletb.2017.07.062.
Tonchev, A. P., Tsoneva, N., Bhatia, C., Arnold, C. W., Goriely, S., Hammond, S. L., Kelley, J. H., Kwan, E., Lenske, H., Piekarewicz, J., Raut, R., Rusev, G., Shizuma, T., & Tornow, W.. Pygmy and core polarization dipole modes in 206Pb: Connecting nuclear structure to stellar nucleosynthesis. United States. doi:10.1016/j.physletb.2017.07.062.
Tonchev, A. P., Tsoneva, N., Bhatia, C., Arnold, C. W., Goriely, S., Hammond, S. L., Kelley, J. H., Kwan, E., Lenske, H., Piekarewicz, J., Raut, R., Rusev, G., Shizuma, T., and Tornow, W.. 2017. "Pygmy and core polarization dipole modes in 206Pb: Connecting nuclear structure to stellar nucleosynthesis". United States. doi:10.1016/j.physletb.2017.07.062.
@article{osti_1373624,
title = {Pygmy and core polarization dipole modes in 206Pb: Connecting nuclear structure to stellar nucleosynthesis},
author = {Tonchev, A. P. and Tsoneva, N. and Bhatia, C. and Arnold, C. W. and Goriely, S. and Hammond, S. L. and Kelley, J. H. and Kwan, E. and Lenske, H. and Piekarewicz, J. and Raut, R. and Rusev, G. and Shizuma, T. and Tornow, W.},
abstractNote = {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±0.2e2fm2 and 8.3±2.0μ$2\atop{N}$, 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±10mb/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 R$206\atop{skin}$=0.12–0.19fm and a corresponding range for the slope of the symmetry energy of L=48–60MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section 205Pb(n,γ)Pb206 at 30 keV to be σ=130±25mb. In conclusion, 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.},
doi = {10.1016/j.physletb.2017.07.062},
journal = {Physics Letters. Section B},
number = C,
volume = 773,
place = {United States},
year = 2017,
month = 8
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.physletb.2017.07.062

Save / Share:
  • 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±0.2e 2fm 2 and 8.3±2.0μmore » $$2\atop{N}$$, 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 α D=122±10mb/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 R$$206\atop{skin}$$=0.12–0.19fm and a corresponding range for the slope of the symmetry energy of L=48–60MeV. This newly obtained information is also used to estimate the Maxwellian-averaged radiative cross section 205Pb(n,γ)Pb 206 at 30 keV to be σ=130±25mb. In conclusion, 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.« less
  • The occurrence of a pygmy dipole resonance in proton rich {sup 32,34}Ar is studied using the unitary correlator operator method interaction V{sub UCOM}, based on Argonne V18. Predictions from the random-phase approximation (RPA) and the shell model in a no-core basis are compared. It is found that the inclusion of configuration mixing up to two-particles-two-holes broadens the pygmy strength slightly and reduces sensibly its strength, as compared to the RPA predictions. For {sup 32}Ar, a clear peak associated with a pygmy resonance is found. For {sup 34}Ar, the pygmy states are obtained close to the giant dipole resonance and mixmore » with it.« less
  • No abstract prepared.
  • The photoresponse of the semimagic N=82 nucleus {sup 136}Xe was measured up to the neutron separation energy S{sub n} using the ({gamma},{gamma}{sup '}) reaction. A concentration of strong dipole excitations is observed well below S{sub n} showing a fragmented resonancelike structure. Microscopic calculations in the quasiparticle phonon model including complex configurations of up to three phonons agree well with the experimental data in the total integrated strength, in the shape and the fragmentation of the resonance, which allows us to draw conclusions on the damping mechanism of the pygmy dipole resonance.