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

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書誌事項

公開日
2017-10
権利情報
  • https://www.elsevier.com/tdm/userlicense/1.0/
  • https://www.elsevier.com/legal/tdmrep-license
  • http://creativecommons.org/licenses/by/4.0/
DOI
  • 10.1016/j.physletb.2017.07.062
  • 10.48550/arxiv.1708.03522
公開者
Elsevier BV

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説明

A high-resolution study of the electromagnetic response of $^{206}$Pb below the neutron separation energy is performed using a ($\vec��$,$��'$) experiment at the HI$\vec��$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 $^{206}$Pb from $4.9$ to $8.1$MeV. The extracted $��$$B$(E1)$\uparrow$ and $��$$B$(M1)$\uparrow$ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9$\pm$0.2e$^2$fm$^2$ and 8.3$\pm$2.0$��_{N}^2$, 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 $^{206}$Pb of $��_{D}\!=\!122\pm10$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 $R_{\rm skin}^{206}\!=\!0.12$-$0.19$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 $^{205}$Pb(n,$��$)$^{206}$Pb at 30keV to be $��\!=\!130\!\pm\!25$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.

8 pages and 4 figures. Manuscript accepted for publication in Physics Letters B

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