Quasielastic Electron Scattering and a Giant Collective State inBi209

Abstract

Inelastic electron scattering from ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ in the momentum transfer range $q=150-300\mathrm{} \frac{\mathrm{MeV}}{c}$ induces a broad, strong excitation at about 20 MeV which cannot be explained by shell-model quasielastic knockout calculations. The excitation form factor exhibits a diffraction pattern whose dependence on $q$ is consistent with preliminary predictions for previously unobserved $E0\mathrm{}$ or $E2\mathrm{}$ giant collective modes in the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ region.