Acta Phys. Hung. A 19/1–2 (2004) 101–108 HEAVY ION PHYSICS Reactions of Massive Nuclei for the Synthesis of Heavy and Superheavy Nuclei G. Giardina, 1 G. Fazio, 1 A. Lamberto, 1 A.I. Muminov, 2 A.K. Nasirov, 2,3 U.T. Yakhshiev, 2 R. Palamara 4 and R. Ruggeri 1 1 Istituto Nazionale di Fisica Nucleare, Sezione di Catania, and Dipartimento di Fisica dell’Universit` a di Messina, Messina, Italy 2 Heavy Ion Physics Department, INP, Tashkent, Uzbekistan 3 Bogoliubov Laboratory of the Theoretical Physics, JINR, Dubna, Russia 4 Dipartimento P.A.U. dell’Universit` a di Reggio Calabria, Reggio Calabria, Italy Received 20 January 2003 Abstract. We study the effect of the entrance channel and the shell struc- ture of reacting massive nuclei on the fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei. In the framework of the combined dinuclear system concept and advanced statistical model, we analyze the reactions 32 S+ 182 W, 48 Ti + 166 Er and 60 Ni + 154 Sm leading to 214 Th * , and the reactions 48 Ca + 248 Cm and the 48 Ca + 249 Cf leading to the 296 116 and 297 118 compound nuclei, respectively. Keywords: fusion, quasifission, superheavy elements PACS: 25.70.Gh, 25.70.-z, 27.90.+b 1. Introduction The difference between measured data on the cross section of evaporation residues for reactions leading to the same compound nucleus can be explained by the dif- ference in the excitation functions of fusion or survival probability of the excited compound nucleus. A decrease of fusion cross sections is connected by an increase of events going to quasifission process. Quasifission reactions are binary processes that exhibit some of the characteristics of fusion–fission events, such as a full relax- ation of the relative kinetic energy and a considerable transfer of mass between the two fragments. The basic difference between fusion–fission and quasifission is that compound nucleus formation is not achieved in the latter mechanism. The DNS concept [1] reveals the reason for the strong decrease in the fusion cross section for a massive system or for a symmetric entrance channel. It is well known that it is 1219-7580/04/ $ 20.00 c  2004 Akad´ emiai Kiad´o, Budapest