Isoscalar Breathing-Mode State inSm144andPb208

Abstract

Inelastic $\alpha$-scattering experiments have been performed on ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at $E_{\alpha }=96\mathrm{}$ MeV over the angular range $3°<~{\theta }_L<~8°$. It is apparent that the isoscalar giant resonance in these nuclei consists of at least two broad components. The angular distribution for one component (${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ $E_x\sim 12.4$ MeV, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ $E_x\sim 11.0$ MeV) is well described as $E2\mathrm{}$, while that for other component (${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$ $E_x\sim 15.1$ MeV, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ $E_x\sim 13.7$ MeV) is well described by an $E0\mathrm{}$ excitation exhausting approximately 100% of the $E0\mathrm{}$ energy-weighted sum rule.