\section{Reaction initial state.}

\hspace{1.0em} The GEANT4 fission model is capable to predict 
final excited fragments as result of an excited 
nucleus  
symmetric or asymmetric fission.  The
fission process (only for nuclei with atomic number 
$A \geq 65$) is considered as a
competitor for evaporation process, when nucleus transits from an
excited state to the ground state. Here we describe the final state generation.
The calculation of the relative probability
of fission with respect to the evaporation channels are described in the chapter
concerning evaporation.

The initial information for calculation of fission
decay consists from the atomic mass number $A$, charge $Z$ of excited
 nucleus, its four momentum $P_0$ 
and  excitation energy $U$.   
