Heavy-ion excitation and photon decay of giant resonances inPb208

We have determined the ground-state photon decay probability and the branching ratios to a number of low-lying states as a function of excitation energy in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ up to ∼15 MeV. Results for the giant quadrupole resonance at 10.6 MeV include determination of a ground-state electromagnetic transition strength B(E2)↑=5800±1600 $e^2$ ${\mathrm{fm}}^4$ and observation of strong suppression of the E1 transition from the resonance to the $3^{\mathrm{-}}$ state at 2.6 MeV. These results confirm the common assumption of the predominately isoscalar character of the 10.6-MeV resonance. Ground-state gamma coincidences enable us to isolate the isovector giant dipole resonance, which is too weak to be seen in singles, and to test models for its excitation in heavy-ion scattering.