Pygmy skin and core polarization modes in Pb isotopes

We have analysed theoretically recent high resolution measurements of the electromagnetic dipole response of ²⁰⁶Pb below the neutron separation energy which was performed at the HIγ→S facility of Duke University. The obtained experimentally spectral distributions and values for the total electric and magnetic dipole strength are compared to EDF+QPM calculations. The detailed theoretical study of the fragmentation pattern of low-energy electric dipole excitations allows for the first time to separate the pygmy dipole resonance from the tail of the giant dipole resonance and multi-phonon excitations showing striking difference of their decay patterns. Furthermore, based on the experiment and the comparison with EDF+QPM and relativistic RPA theories, the dipole polarizability α_D=122.18±9.72 mb/MeV and the neutron skin thickness r_skin=0.151 fm in ²⁰⁶Pb are extracted. The newly obtained experimental and theoretical information is used to predict the Maxwellian-averaged cross section of the ²⁰⁵Pb(n,γ^')²⁰⁶Pb reaction at 30 keV. The astrophysical impact of different counterparts of the electric and magnetic dipole spectra related to the s-process of stellar nucleosynthesis is discussed.