The fine structure of the low-energy octupole resonance was studied for ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ by proton inelastic scattering at $E_{\mathrm{p}=65\mathrm{}}$ MeV. The low-energy octupole resonance was composed of many discrete levels of L=3 states. The total energy-weighted sum rule fraction of more than 10% was found in every nucleus. Especially in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, the energy-weighted sum rule fraction amounted to 15%. The strength was finely fragmented in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, but less fragmented in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. It is suggested that the ‘‘degree of fragmentation’’ is correlated with the excitation energy and the distribution of the low-lying quadrupole phonon states.

• Received 14 February 1985

DOI:https://doi.org/10.1103/PhysRevC.32.425