Coulomb nuclear interference as a tool to investigate the nuclear potential

The sub-barrier excitation function of the octupole vibrational state at 2.615 MeV in Pb208 is analyzed within the coupled-channels framework. It is shown that the position of the minimum in the excitation function, which is due to the destructive interference of the Coulomb and nuclear scattering amplitudes, is very sensitive to the nuclear potential for both the ground state and the octupole state. A different nuclear potential for the 3- state may arise from changes in the matter distribution of Pb208 due to the particle-hole excitations. The present analysis places a strong limit on the 3- nuclear potential diffuseness, giving a difference of only Δa0=0.011±0.004 fm between the ground state and 3- state diffuseness.