Neutron rich clusters and the dynamics of fission and fusion

The report discusses experimental evidence for the appearance of cluster aspects in the dynamics of large rearrangement processes, as fusion and fission. Clusters here are the strongly bound doubly magic nuclei and the superheavy nucleus 298114184. Two of them, 78Ni and 298114, have not yet been identified. There is no evidence from fission or fusion that the Z=28-shell plays any role. But Ni-isotopes are produced in fission, and will be used for the synthesis of elements 110 and 111. 48Ca is discussed in connection with the 208Pb-based fusion reactions. Experiments where it acts as a cluster in rearrangement processes independently are not known. The discussion in this report is thus reduced to the closed-shells with N=50, 82, and 126 and Z=50 and 82. With increasing nucleon numbers, the shell corrections to the binding energies increase, and the strongest effects are to be expected for these shells. The 132Sn-cluster dominates low energy fission, and the 208Pb-cluster gave a new radioactivity and the heaviest elements 107 to 109. Experimental findings from heavy element production are outlined, and then the stability of cluster aspects to intrinsic excitation energy in fusion and fission is discussed. The importance of compactness of the clustering system seems to be equally decisive in fission and fusion, and it may be a key to the understanding of the making of the heaviest elements. (N.K.)