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

The estimated collective velocities in λ and ε are large enough to consider diabatic effects
in the DNS. We estimated the minimal excitation energy per nucleon ε ∗ for the applicability <strong>of</strong>
the diabatic treatment. The value <strong>of</strong> ε ∗ must fulfill the following inequality [52]
ε ∗ ≥ (1.4 × 10 −22 MeV s)
2π|Hαβ |2
¯h|∂ɛαβ /∂ q|κ
, (3.6)
where κ is the mean distance in q between two subsequent crossings. The numerical factor in
(3.6) is obtained by using the Fermi-gas model for estimating the decay time due to residual
two-body collisions [52]. From the study <strong>of</strong> the diabatic and adiabatic levels <strong>of</strong> the systems
considered, we obtained ε ∗ ≥0.03 MeV for the relative motion in R and ε ∗ ≥ 0.07 MeV for
the motion in the neck coordinate ε. Therefore, the diabatic effects are already important for
relatively small excitation energies <strong>of</strong> 6—14 MeV. For the relative motion, the averange values
<strong>of</strong> the coupling |Hαβ| and <strong>of</strong> the difference |∂ɛαβ/∂R| in the slopes <strong>of</strong> the crossing levels are
0.17 MeV and 1.52 MeV/fm, respectively. The value <strong>of</strong> the coupling |Hαβ| is estimated as the
half <strong>of</strong> the difference <strong>of</strong> energies <strong>of</strong> the adiabatic levels α, β at the pseudo-crossing point. For
the motion in the neck coordinate, we obtained |Hαβ| =0.2 MeV and |∂ɛαβ/∂ε| =0.77 MeV.
Since in Ref. [52] the diabatic single particle spectra were calculated with another Hamiltonian,
a larger minimal value <strong>of</strong> ε ∗ was obtained.
In the present chapter we studied diabatic potentials as a function <strong>of</strong> elongation, neck
coordinate and mass asymmetry for various heavy systems. The calculations were performed
using the maximum symmetry method with the generalized TCSM. The diabatic effects give
rise to hindrances for the growth <strong>of</strong> the neck and for the motion to smaller relative distances.
The diabatic potentials as a function <strong>of</strong> the elongation are similar to the phenomenological
double folding potentials used in the DNS model <strong>of</strong> fusion, which describes the experimental
data quite well. For the asymmetric DNS, the diabatic hindrance for the motion to smaller
elongations is smaller than for the symmetric DNS and, therefore, its evolution to the compound
nucleus in λ is more favored. The quasi-fission barrier becomes larger with the increase <strong>of</strong> the
mass asymmetry in the entrance channel. The temperature decreases the repulsive character
<strong>of</strong> the diabatic potential. The diabatic TCSM supports the model <strong>of</strong> fusion based on the DNS
concept, where a hindrance for the motion to smaller values <strong>of</strong> λ is assumed. The diabatic
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