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

Tonchev, A.P.  ,  Tsoneva, T.  ,  Bhatia, C.  ,  Arnold, C.W.  ,  Goriely, S.  ,  Hammond, S.L.  ,  Kelley, J.H.  ,  Kwan, E.  ,  Lenske, H.  ,  Piekarewicz, J.  ,  Raut, R.  ,  Rusev, G.  ,  静間, 俊行  ,  Tornow, W.

773pp.20 - 25 , 2017-08
A high-resolution study of the electromagnetic response of 206Pb below the neutron separation energy is performed using a (g,g) experiment at the HIgS 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 4.9to 8.1 MeV. The extracted B(E1) ↑ and B(M1) ↑ values for the total electric and magnetic dipole strength below the neutron separation energy are 0.9 ± 0.2e2 fm2 and 8.3 ± 2.0μ2N , 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 aand 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 205Pb(n, γ )206Pb 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.

Number of accesses :  

Other information