Direct Evidence for a New Giant Resonance at80A−13MeV in the Lead Region

Abstract

Inelastic $\alpha$ scattering experiments at 120 MeV on ${}_{}{}^{206,208}{}_{}{}^{}\mathrm{Pb}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ reveal the existence of a new isoscalar resonance located at $\sim 80A^{-\frac{1}{3}}$ MeV in addition to the well-known resonance at $\sim 63A^{-\frac{1}{3}}$ MeV. The angular distribution of this new resonance, though not inconsistent with an $E4\mathrm{}$ assignment, is better described by $E0\mathrm{}$ or $E2\mathrm{}$. It would exhaust approximately 100%, 50%, or 17% of the corresponding isoscalar $E0\mathrm{}$, $E2\mathrm{}$, or $E4\mathrm{}$ energy-weighted sum rules, respectively.