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

Chapter 4
The evolution <strong>of</strong> the dinuclear system (DNS) proceeds along a large number <strong>of</strong> trajectories
in the configuration space. The mass (charge) asymmetry η =(A1 − A2)/(A1 + A2) (ηZ =
(Z1 − Z2)/(Z1 + Z2)) (A1 (Z1) andA2 (Z2) are the mass (charge) numbers <strong>of</strong> two nuclei) and
the distance R between the centers <strong>of</strong> nuclei (or the elongation λ <strong>of</strong> the system) are assumed to
be the most important degrees <strong>of</strong> freedom in the DNS [18, 34]. The preferable fusion channel in
the DNS model [18, 34] is the evolution <strong>of</strong> the DNS to a compound nucleus by nucleon transfer
from a light nucleus to a heavy one, the motion to larger η at the touching configuration <strong>of</strong>
the nuclei. In this model the melting <strong>of</strong> nuclei in the relative distance R is strongly hindered.
This hindrance can be explained by a structural forbiddenness effect [36], by diabatic effects
for the motion <strong>of</strong> the system to smaller relative distance [35, 66] and by a large microscopical
mass parameter for the growth <strong>of</strong> the neck [43]. The dynamics <strong>of</strong> the DNS is ruled by the
potential energy surface which depends on the isotope composition, on the structure <strong>of</strong> the
fragments determining the transfer processes and collective excitations, and on the division <strong>of</strong>
the excitation energy between the nuclei.
In this chapter, we compare the potential energy U as a function <strong>of</strong> η at the touching
configuration <strong>of</strong> the nuclei (driving potential) obtained with different methods. The value <strong>of</strong>
R for the touching configuration is determined by η and by deformations <strong>of</strong> the DNS nuclei.
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