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

where B1, B2, andB12 are the binding energies <strong>of</strong> the fragments and the compound nucleus,
respectively, and are calculated with liquid-drop masses for large excitation energies and with
realistic masses [68] for small excitation energies. The value <strong>of</strong> U(R, η, ηZ) is normalised to the
binding energy B12 <strong>of</strong> the compound nucleus. The nucleus-nucleus potential V (R, η, ηZ) in(4.1)
includes the Coulomb and nuclear terms. The nuclear part <strong>of</strong> the nucleus-nucleus potential is
calculated using a double-folding procedure [65]. The phenomenological driving potential is
obtained as U(η) =U(Rm,η,ηZ), where Rm = R1 + R2+0.5 fm (Ri is the radius <strong>of</strong> the nuclei)
is the distance between the centers <strong>of</strong> interacting nuclei corresponding to the minimum <strong>of</strong> the
pocket in the nucleus-nucleus potential V (R, η, ηZ). For heavy systems and small values <strong>of</strong> the
angular momentum, the influence <strong>of</strong> the rotational energy is negligible [34, 69]. Deformation
effects are taken into account in the calculation <strong>of</strong> V (R, η, η Z) [34]. The heavy nuclei in the
DNS, which are deformed in the ground state, are treated with the parameters <strong>of</strong> quadrupole
deformation taken from Refs. [70, 71]. The light nuclei <strong>of</strong> the DNS are assumed to be deformed
only if the energy <strong>of</strong> their 2 + state is smaller than 1.5 MeV. As known from experiments on
sub—barrier fusion <strong>of</strong> lighter nuclei [72], these states are easily populated. For the collision
energies considered here (above and near the Coulomb barrier), the relative orientation <strong>of</strong> the
nuclei in the DNS follows the minimum <strong>of</strong> the potential energy.
4.1.2 TCSM-method
The driving potential is calculated using the adiabatic TCSM (3.2) because the diabatic effects
are small near the touching configuration <strong>of</strong> the nuclei. Since we consider small excitation ener-
gies (20−30MeV), for which the shell effects remain important, the dependence <strong>of</strong> δU shell and
δU pair on the temperature is disregarded here. The isotopic composition <strong>of</strong> the nuclei forming
the DNS is chosen with the condition <strong>of</strong> N/Z- equilibrium in the system. The deformations
β i = a i/b i <strong>of</strong> the DNS nuclei are calculated from their semiaxes a i and b i (see Appendix). The
semiaxes a i and b i <strong>of</strong> the nuclei can be related to the parameter <strong>of</strong> the quadrupole deformation
[70, 71] using the known expansion <strong>of</strong> the nuclear surface in spherical functions. The neck
parameter ε is 0.74, which supplies realistic shapes <strong>of</strong> the DNS for the touching configuration
<strong>of</strong> the nuclei (λ =1.5 − 1.6) .
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