Signatures of ssion dynamics in highly excited nuclei produced in Au(800 A MeV) on proton collisions

197Au(800 A MeV)-on-proton collisions are used to investigate the ssion dynamics at high excitation energy. The kinematic properties together with the isotopic identi cation of the ssion fragments allow to determine the mass, charge and excitation energy of the ssioning nucleus at saddle. The comparison of these observables and the measured total ssion cross section with model calculations evidences a clear hindrance of ssion at high excitation energy that can be explained in terms of nuclear dissipation. Assuming a statistical evaporation for other de-excitation channels than ssion, an estimated value of the transient time of ssion of (3 1) 10 21 s is obtained.