Excitation of giant resonances inPb208andAu197via proton inelastic scattering

The giant resonance regions in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ have been investigated by inelastic scattering of 61-MeV protons with an energy resolution of about 100 KeV. Cross sections for the giant quadrupole resonance at $E_x\approx 63A^{-\frac{1}{3}}$ MeV exhaust 90±15% of the energy-weighted sum-rule strength for an isoscalar $E2\mathrm{}$ excitation in both nuclei. The angular distribution for the giant quadrupole plus giant dipole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ is compared with microscopic-model distroted-wave Born approximation calculations. A pronounced fine-structure resonance is observed in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at $E_x\approx 56A^{-\frac{1}{3}}$ MeV (9.4 MeV). The angular distribution for this resonance is well described by distroted-wave Born approximation calculations for an $E2\mathrm{}$ or $E3\mathrm{}$ excitation, but not for an $E0\mathrm{}$ excitation. No prominent fine-structure resonances are observed in ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$. The spectra in the bound-state region for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ show a pronounced structure centered at $E_x\approx 4$ MeV, for which the angular distribution is best described by distorted-wave Born approximation calculations for $E3\mathrm{}$ or $E4\mathrm{}$ excitations.