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

a behaviour correlates with the diabatic contributions to the potential energy [35]. The
Such
arise from the factor fluctuations ˜
k /Γ f 2 in Eq. (5.32) and are related to the increasing number
k
<strong>of</strong> crossings between the single particle levels near the Fermi level with decreasing λ [35].
The choice <strong>of</strong> the width <strong>of</strong> the single particle levels is crucial for the value <strong>of</strong> M diag in
the diabatic and adiabatic cases within a reasonable variation. If instead <strong>of</strong> Γ both −1
0 =0.045
MeV−1 the value <strong>of</strong> Γ , −1
is taken as 0.03 MeV 0 −1 the lower limit , the value <strong>of</strong> Mεε becomes
at
times smaller, but remains larger than M 2.25 WW
εε
about one order <strong>of</strong> magnitude. For larger
by
the average width Γ increases and the function temperatures, ˜
k /Γ f 2
k
becomes smoother. The
mass parameter M εε depends on temperature T0 mainly due to the width Γ k <strong>of</strong> the single-
levels ( Γk ∼ T particle 2 0 ). The value <strong>of</strong> M decreases with T εε −4
. One- and two-body inter-
0
actions [96] contribute to the nondiagonal and diagonal parts <strong>of</strong> the mass parameter, respec-
tively. Whereas the one-body contribution to mass (nondiagonal part) is relatively insensitive
to the temperature <strong>of</strong> the system, the two-body contribution to mass (diagonal part) increases
strongly with decreasing temperature. The two-body interaction is considered in our calcu-
lations using the width <strong>of</strong> the single-particle levels [86]. So, we can observe in Fig. 5-7 that
M diag
εε
=1MeV )/M (T0 diag(T0
=1.5MeV) ∼ 5 on average for the values <strong>of</strong> ε =0.5− εε
. We 1
that the contribution <strong>of</strong> the diagonal part M found diag to Mεε is the largest at quite a high
εε
excitation energy <strong>of</strong> 30MeV (T0 =1.3MeV ) <strong>of</strong> the DNS in fusion reactions. For comparison,
the excitation energies <strong>of</strong> the initial DNS are smaller than 20MeV (T0 < 1.0MeV )inPb− and
Bi− based cold fusion reactions. Hot fusion reactions <strong>of</strong> heavy nuclei have excitation energies
<strong>of</strong> the initial DNS smaller than 40MeV (T0 =1.5MeV ) and a rapid decrease <strong>of</strong> the survival
probability <strong>of</strong> the compound nucleus with increasing excitation energy. Finally, we should stress
that the mass parameter M εε remains always much larger (e.g., 20−30 times for T0 =1.3MeV)
in fusion reactions than the mass calculated with the hydrodynamical Werner-Wheeler approx-
imation for T0 =1− 1.5MeV.
The mass parameters at the touching configuration <strong>of</strong> the nuclei are the same in the adia-
batic and diabatic descriptions because the single particle levels and occupation numbers are
practically the same in these two limits. It is known that the mass parameters are smaller in
the diabatic case for a zero width <strong>of</strong> single particle levels than in the adiabatic case [57]. We
found values for the mass parameters M λλ and M εε within the diabatic TCSM which are closer
75