ar X iv : n uc l - th / 9 91 10 09 v 1 2 N ov 1 99 9 DINUCLEAR CONCEPT – CLUSTER MODEL OF FUSION

The synthesis of superheavy elements is analysed within the dinuclear system concept of compound nucleus formation. The perspectives for using radioactive beams in complete fusion reactions are discussed. The existing fusion models are distinguished by the choice of the relevant collective degree of freedom which is mainly responsible for the complete fusion. For example, many models assume a melting of the nuclei along the relative distance. It was demonstrated that the adiabatic scenario of fusion in the relative distance leads to an overestimation of the fusion probability P CN 1 and mostly gives an incorrect isotopic trend of P CN. In the dinuclear system (DNS) concept 2 the compound nucleus is reached by a series of transfers of nucleons from the light nucleus to the heavy one. The dynamics of the DNS is considered as a combined diffusion in the degrees of freedom of the mass asymmetry η = (A 1 − A 2)/(A 1 + A 2) (A 1 and A 2 are the mass numbers the DNS nuclei) and of the relative distance describing the formation of the compound nucleus and the quasifission process (decay of the DNS), respectively 3. The competition between the complete fusion and quasifission processes is taken into consideration in the DNS model and leads to a strong reduction of the fusion cross section 3,4. This cluster fusion model is justified by the structural forbiddenness effect 5 which hinders the nuclei to melt together along the relative distance. In the DNS concept 3 the evaporation residue cross section is calculated as σ ER = J σ c P CN W sur , where σ c is the capture cross section for angular momentum J. The stabilizing shell effects of the formed superheavy compound nucleus against fission in the de-excitation process are thoroughly studied by the theory and surviving probabilities W sur of compound nuclei are derived. The dependence of the probability of complete fusion P CN on nuclear structure effects during the fusion process starting from the entrance channel and ending with the compound nucleus formation is the crucial factor for the correct calculation of σ ER. Xe the fusion probabilities are decreased 6 when the neutron number of projectile or target deviates from the magic number. In the DNS model this behaviour is simply 1