Fusion of heavy deformed nuclei

Evaporation residues produced in the fusion reactions of 60,64Ni on 154Sm and 76Ge on 150Nd were measured near Coulomb barrier energy by using JAERI-RMS. It was found that the fusion probability depends on the orientation of the deformed targets. When the projectiles collide at the tip of the deformed nuclei, the fusion probability is considerably reduced to the amount of 1/100-1/1000 of the predictions. On the other hand, when the projectiles collide at the side of the deformed nuclei, the fusion occurs without any hindrance. This phenomenon was understood qualitatively by comparing the distance between mass centers of two colliding nuclei at the touching configuration with the position of the saddle point of the compound nucleus. When the distance is longer than the saddle position, the fusion is hindered and an extra-extra push energy is needed to evolve into the formation of the compound nucleus. (author)