LNGS particle physics laboratory. OPERA (Oscillation Project with Emulsion-tRacking Apparatus) neutrino experiment inside Hall C of the Laboratori Nazionali del Gran Sasso (Gran Sasso National Laboratory, LNGS), Italy. This particle physics laboratory lies near Gran Sasso mountain, which shields the LNGS experiments from outside radiation, allowing particle physicists and astrophysicists to study rare interactions involving neutrinos and other particles, in a low background environment. OPERA studies nuclear emulsions made of micro-crystals of silver halides (AgBr) dispersed in a gelatin layer.