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Caption: CERN detector, 1977. Researcher examining a spark chamber detector at CERN, the European particle physics laboratory, Switzerland. A spark chamber detects particles as they ionize a gas inside the chamber. These ions then trigger the high-voltage electrodes in the chamber, forming a visible spark that is recorded by camera. The particles, which are produced during collisions of other particles accelerated to high energies, are studied in order to understand the fundamental structure of matter. Many key discoveries in particle physics have been made at CERN, which was founded in 1954.