Experimental set-up and first results of the experiment concerning the dynamics of the fussion-fission reactions are presented. The analysis was performed for the reactions: ⁸Si + ⁹⁸Mo and ¹⁹F + ¹⁰⁷Ag leading to the same complete fusion nucleus ¹²⁶Ba. The fission fragments and the emitted neutrons were simultaneously measured. The experimental data contain information about the masses and velocities of the fragments and about the angular and energy distributions of emitted neutrons.