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

Chapter 7
In the quasi-fission process, the large mass rearrangements between the interacting heavy ions
occur at a short time scale [11, 112]. One <strong>of</strong> the experimental signatures [113] <strong>of</strong> this process
is the large width <strong>of</strong> mass distributions, incompatible with compound nucleus fission. Con-
ceptually, the quasi-fission bridges the gap [106] between the deep-inelastic collisions, where
the reaction partners get into sufficiently close contact to exchange many particles practically
without altering their average mass and charge [33], and the complete fusion process, where
the reaction partners completely lose their identity by transformation into a compound nucleus
[113]. All these types <strong>of</strong> reaction are organically connected and are derived from the evolu-
tion <strong>of</strong> a dinuclear system (DNS) [18, 34] which is formed in the entrance channel during the
capture stage <strong>of</strong> reaction, after the dissipation <strong>of</strong> the collision kinetic energy. The decay <strong>of</strong>
the DNS when it evolves in the mass asymmetry coordinate predestines the charge and mass
distributions <strong>of</strong> the reaction products. The competition between the complete fusion and the
quasi-fission process occurs in reactions with massive nuclei at low bombarding energies (< 15
MeV/u) [34].
In this chapter, the quasi-fission process is described as the evolution <strong>of</strong> the DNS in the Z
(A) coordinate by nucleons transfer between nuclei taking into account the DNS decay in the
internuclear distance R (or elongation λ). Here, Z (A) denotes the charge (mass) number <strong>of</strong> the
light fragment <strong>of</strong> the DNS. For the sake <strong>of</strong> simplicity, we will use the variables Z(A) instead <strong>of</strong> the
charge (mass) asymmetry η (ηZ). Since the isotopic composition <strong>of</strong> the nuclei forming the DNS
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