Evidence of double phonon excitations in the fusion of Pb

The fusion cross-sections for , measured to high precision, enable the extraction of the distribution of fusion barriers. This shows a structure markedly different from the single barrier which might be expected for fusion of two doubly-closed shell nuclei. The results of exact coupled-channel calculations performed to understand the observations are presented. These calculations indicate that coupling to a double octupole phonon excited state in is necessary to explain the experimental barrier distributions.