The Big European Bubble Chamber is a large size detector formerly used to study particle physics at CERN. The chamber body, a stainless-steel vessel, was filled with 35 cubic metres of superheated liquid hydrogen, liquid deuterium or a neon-hydrogen mixture, whose sensitivity was regulated by means of a movable piston weighing 2 tons. The liquids at typical operation temperatures around 27 K were placed under overpressure of about 5 atm. The piston expansion, synchronized with the charged particle beam crossing the chamber volume, caused a rapid pressure drop with in consequence the liquid reaching its boiling point
During each expansion, charged particles ionized the atoms of the liquid as they passed through it and the energy deposited by them initiated boiling along their path leaving trails of tiny bubbles. These bubbles tracks were photographed by the five cameras mounted on top of the chamber. The stereo photographs were subsequently scanned and all events finally evaluated by a team of scientists. After each expansion, the pressure was increased again to stop the boiling. The bubble chamber was then ready again for a new cycle of particles beam exposure.