Effects of diabaticity on fusion of heavy nuclei in the dinuclear model ...

experiment have to be developed to describe the extremely small fraction <strong>of</strong> the total cross
section leading to fusion. Predictions based on these models are useful in the preparation <strong>of</strong> the
next generation <strong>of</strong> experiments. The macroscopic models ([14], [15], [16]) do not reproduce the
excitation function <strong>of</strong> the reactions used for the synthesis <strong>of</strong> superheavy elements. Compensat-
ing the dissipative losses in the relative motion, the macroscopical dynamical model (MDM) <strong>of</strong>
Swiatecki [16] and the surface friction model by Fröbrich [15] have to take an extra-extra-push
energy into account leading to an excitation energy <strong>of</strong> the compound nucleus which results too
large compared to the experimental data for superheavy elements [17]. In addition, the MDM
concept yields too large evaporation residue cross sections as demonstrated for example for the
100 Mo + 100 Mo and 110 Pd + 110 Pd reactions [18] since the MDM does not take into account
the competition between complete fusion and quasi-fission processes. In the MDM, the follow-
ing qualitative picture was considered: i) after the capture, the neck between the nuclei grows
quite quickly and a deformed united system is formed; (ii) the united system either overcomes
the saddle point and moves to the equilibrium state <strong>of</strong> the compound nucleus or goes to the
quasi-fission channel. The choice <strong>of</strong> the channel <strong>of</strong> complete fusion or quasi-fission depends on
the initial kinetic energy <strong>of</strong> the projectile.
Another method to calculate fusion cross sections is based on the dinuclear system (DNS)
concept [19]. Within this concept, calculations <strong>of</strong> the complete fusion probability and optimal
excitation energy for the production <strong>of</strong> compound nuclei between Z=102 and Z=114 are in
agreement with the experimental data ([20], [21] and [22]). The model based on the DNS-
concept gives an explanation <strong>of</strong> the reduction <strong>of</strong> the fusion cross sections by quasi-fission and
can be used for the prediction <strong>of</strong> evaporation residue cross sections in the production <strong>of</strong> heavy
and superheavy elements by cold and hot fusion reactions [22]. The main idea <strong>of</strong> the DNS-
concept is the assumption that complete fusion and deep inelastic transfer reactions are similar
nuclear processes. Both <strong>of</strong> them are realized according to similar scenarios. The scenario <strong>of</strong>
the complete fusion process is as follows. At the capture stage, after full dissipation <strong>of</strong> the
collision kinetic energy, the DNS is formed. The complete fusion process is the DNS evolution
that proceeds via nucleon transfer, shell by shell from one nucleus to the other. The DNS nuclei
retain their individuality throughout their way to the compound nucleus. This peculiarity <strong>of</strong>
the DNS evolution is the consequence <strong>of</strong> the shell structure <strong>of</strong> the nuclei.
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