Barrier distribution of quasi-elastic backward scattering in very heavy reaction systems

Mitsuoka, Shinichi; Ikezoe, Hiroshi; Nishio, Katsuhisa   ; Watanabe, Yutaka*; Jeong, S. C.*; Ishiyama, Hironobu*; Hirayama, Yoshikazu*; Imai, Nobuaki*; Miyatake, Hiroari

We have measured quasi-elastic scattering cross sections in reactions of Ti, Cr, Fe, Ni and Zn + Pb, relating to Pb-based cold fusion reactions for super-heavy elements 104, 106, 108, 110 and 112, respectively. A thin target of Pb was bombarded by heavy-ion beams supplied from the JAEA tandem-booster accelerator with changing the beam energy in steps of 1.5 MeV. The barrier distributions were derived from the first derivative of the excitation functions measured at backward angles of 172, 168 and 162. The centroid of the barrier distributions showed a deviation from several predicted barrier heights toward the low energy side. The shape of the barrier distributions was well reproduced by the results of a coupled-channel calculation taking account of the coupling effects of the collective vibrational excitations in the projectile and target nuclei. We have recently obtained similar results in heavier reactions of Ge and Kr + Pb.