Proton decay experiment to determine the ultimate stability of matter. View of the entrance to the French side of the Mont Blanc tunnel, inside which is located the NUSEX proton decay experiment. The tunnel runs between France & Italy under Mont Blanc. NUSEX is located several kilometers inside the tunnel, on the French side of the border, in one of the garage areas dug out of the rock at regular intervals along the tunnel. .View of the NUSEX (Nucleon Stability Experiment) proton decay detector located in a garage area off the Mont Blanc tunnel under some 5000 meters of rock which shields it from most cosmic radiation. (1985)