  The relevance of equilibrium in a multifragmentation reaction of very central
$^{40}Ca+^{40}Ca$ collisions at 35 MeV/nucleon is investigated by using
simulations of Antisymmetrized Molecular Dynamics (AMD). Two types of ensembles
are compared. One is the reaction ensemble of the states at each reaction time
$t$ in collision events simulated by AMD, and the other is the equilibrium
ensemble prepared by solving the AMD equation of motion for a many-nucleon
system confined in a container for a long time. The comparison of the ensembles
is performed for the fragment charge distribution and the excitation energies.
Our calculations show that there exists an equilibrium ensemble which well
reproduces the reaction ensemble at each reaction time $t$ for the investigated
period $80\leq t\leq300$ fm/$c$. However, there are some other observables
which show discrepancies between the reaction and equilibrium ensembles. These
may be interpreted as dynamical effects in the reaction. The usual static
equilibrium at each instant is not realized since any equilibrium ensemble with
the same volume as that of the reaction system cannot reproduce the fragment
observables.

Nuclear Theory