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

estimated from the difference between the bombarding energy Ec.m. in the system <strong>of</strong> the center
<strong>of</strong> mass and the value <strong>of</strong> the nucleus-nucleus potential for R corresponding to the bottom <strong>of</strong> the
pocket for the initial configuration <strong>of</strong> the DNS. The charge (mass) quasi-fission distributions
slightly on the excitation energy E depend ∗ the initial DNS (Fig. 7-1). This is due to the
<strong>of</strong>
dependence <strong>of</strong> the transport coefficients ∆ weak (±)
the temperature [33]. With an increasing
on
temperature <strong>of</strong> the system, the influence <strong>of</strong> the shell effects on the process <strong>of</strong> nucleon transfer
decreases more slowly than the exponential decrease <strong>of</strong> the shell correction in the potential
energy [33]. It was experimentally found [113] in the quasifission reactions 238 U+ 16 O, 26 Mg,
27 Al, 32 S, 35 Cl, 40,48 Ca and nat Zn at several bombarding energies, that the mass asymmetry
motion is dominated by the one-body dissipation which is independent <strong>of</strong> temperature. The
observed relaxation times for the mass asymmetry mode <strong>of</strong> all the systems considered were in
agreement with the wall dissipation picture [113].
Z
Fig. 7-3 shows the quasi-fission charge and mass distributions for the cold fusion reactions
with the projectiles 50 Ti, 64 Ni and 76 Ge on the target 208 Pb, which lead to the synthesis <strong>of</strong> the
elements 258 104, 272 110 and 284 114, respectively, with an excitation energy about 11-16 MeV [7,
8]. The ratio between the drifts <strong>of</strong> mass and charge toward symmetric configurations <strong>of</strong> the DNS
and toward more asymmetric ones becomes considerably larger with the increase <strong>of</strong> the charge
number <strong>of</strong> the superheavy element. Due to this fact, the complete fusion probability in the mass
asymmetry degree <strong>of</strong> freedom decreases from the nucleus 258 104 to 272 110. For the reaction
76 Ge+ 208 Pb→ 284 114, we found that the quasi-fission products are practically associated with
fragmentations near the initial DNS due to small values <strong>of</strong> quasi-fission barriers B qf. Comparing
Fig. 7-3 with Fig.7-2, we see that the mass and charge yields <strong>of</strong> the quasi-fission products for
nearly symmetric configurations <strong>of</strong> the DNS are larger for the hot fusion reaction 48 Ca+ 244 Pu
than for the cold fusion reaction 76 Ge+ 208 Pb. The quasi-fission barrier B qf <strong>of</strong> the initial DNS
becomes larger with decreasing Z, and the nucleon transfer plays a larger role in the evolution
<strong>of</strong> this DNS than the decay process. This is consistent with the conclusion that the hot fusion
reaction 48 Ca+ 244 Pu→ 292 114 is preferable for the synthesis <strong>of</strong> the element 114, although the
survival probability <strong>of</strong> the compound nucleus decreases with increasing excitation energy [20,
22]. In the cold fusion reactions, the quasi-fission is an important factor decreasing the complete
fusion cross sections with increasing atomic number <strong>of</strong> the superheavy element. Producing the
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