HEAVY CLUSTERS IN COLD NUCLEAR REARRANGEMENTS IN FUSION AND FISSION

The experimental evidence for the appearance of cluster aspects in the dynamics of large rearrangement processes, as fusion and fission, is presented. Clusters in the sense as used in the following are strongly bound, doubly magic neutron rich nuclei as Ca-48(28), Ni-78(50), Sn-1 32(82), and Pb-208(126), the spherical nuclei Z = 114 - 126 and N = 18 4, and nuclei with closed shells N = 28, 50, 82, and 126, and Z = 28, 50, and 82. As with increasing nucleon numbers, the absolute shell cor rections to the binding energies increase, the strongest effects are t o be observed for the higher shells. The Sn-132 cluster manifests itse lf in low energy fission (FAISSNER H. and WILDERMUTH K., Nucl. Phys., 58 (1964) 177). The Pb-208 cluster gave us the new radioactivity (ROSE M. J. and JONES G. A., Nature, 307 (1984) 245) and the first superhea vy elements (SHE) (ARMBRUSTER P.,Ann. Rev. Nucl. Part. Sci., 35 (1985) 135-94; MUNZENBERG G., Rep. Progr. Phys., 51 (1988) 57). I will discu ss experiments concerning the stability of clusters to intrinsic excit ation energy in fusion and fission (ARMBRUSTER P., Lect. Notes Phys, 1 58 (1982) 1), and the manifestation of clusters in the fusion entrance channel (ARMBRUSTER P., J. Phys. Sec. Jpn., 58 (1989) 232). The impor tance of compactness of the clustering system seems to be equally deci sive in fission and fusion. Finally, I will cover the importance of cl usters for the production of SHEs.