Evidence for the Isoscalar Giant Dipole Resonance in ${}^{208}\mathrm{Pb}$ Using Inelastic $\alpha$ Scattering at and near 0°

The isoscalar giant dipole resonance (ISGDR) in ${}^{208}\mathrm{Pb}$ has been investigated using inelastic scattering of 200 MeV $\alpha$ particles at and near 0° where the angular distribution of the ISGDR can be clearly differentiated from those of other modes. The “difference of spectra” technique was employed to separate the ISGDR from the high-energy octupole resonance (HEOR). These data provide the clearest evidence yet for the ISGDR adjacent to the HEOR. With these results, all expected isoscalar $\lambda \le 3$ resonances in ${}^{208}\mathrm{Pb}$ have been identified.