  By using the improved Quantum Molecular Dynamics model, the
$^{244}$Pu+$^{244}$Pu, $^{238}$U+$^{238}$U and $^{197}$Au+$^{197}$Au reactions
at the energy range of $E_{c.m.}$=800 $MeV$ to 2000 $MeV$ are studied. We find
that the production probability of superheavy fragments(SHF) with $Z \geq$ 114
is much higher for $^{244}$Pu+$^{244}$Pu reaction compared with that of
$^{238}$U+$^{238}$U reaction and no product of SHF is found for
$^{197}$Au+$^{197}$Au. The production probability of SHF is narrowly peaked in
incident energy dependence. The decay mechanism of the composite system of
projectile and target and the time scale of decay process are explored. The
binding energies of superheavy fragments are found to be broadly distributed
and their shapes turn out to be exotic form.

Nuclear Theory