The electric dipole polarizability ${\alpha }_D$ and the neutron-skin thickness $\mathrm{\Delta }{R}_{np}$ of ${}^{208}\mathrm{Pb}$ are two powerful and clean probes for constraining the symmetry energy at subsaturation densities. Within the framework of the antisymmetrized molecular dynamics (AMD) model, the width of the strength function and its dynamical origins are understood, and the ${\alpha }_D$ and $\mathrm{\Delta }{R}_{np}$ data favor effective interaction parameter sets with $S_0\approx 32–34$ MeV and $L=64–87$ MeV. In addition, our calculations show that the sensitive densities of ${\alpha }_D$ and $\mathrm{\Delta }{R}_{np}$ range from $0.2{\rho }_0$ to $0.57{\rho }_0$, and the corresponding values of the symmetry energy at the lower and upper ends of this sensitive density region are $S\left(0.2{\rho }_0\right)=10.18\pm 1.10$ MeV and $S\left(0.57{\rho }_0\right)=22.31\pm 1.32$ MeV.

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• Coulomb excitation
• Electromagnetic transitions
• Models & methods for nuclear reactions
• Neutron skin thickness
• Nuclear charge distribution
• Nuclear reactions
• Photonuclear reactions
• Resonance reactions
• Symmetry energy
• Nuclear many-body theory