Barrier distribution of quasi-elastic backward scattering

In order to study the nucleus‐nucleus interaction in Pb‐based cold fusion, we have measured excitation functions for quasi‐elastic scattering of 48Ti, 54Cr, 56Fe, 64Ni, 70Zn and 86Kr projectiles on 208Pb target at backward angles. The barrier distributions were derived from the first derivative of measured quasi‐elastic scattering cross sections relative to the Rutherford scattering cross section. The centroids of the barrier distributions show a deviation from several predicted barrier heights toward the low energy side. The shape of the barrier distributions is well reproduced by the results of a coupled‐channel calculation taking account of the coupling effects of two phonon excitations of the quadrupole vibration for the projectiles and of the octupole vibration for the 208Pb target.