spark chamber

Electronic device for recording tracks of charged subatomic particles, decay products, and rays. At its simplest, it consists of two smooth threadlike electrodes that are positioned 1-2 cm/0.5-1 in apart, the space between being filled with a mixture of neon and helium gas. Sparks jump through the gas along the ionized path created by the radiation. More usually, the detector consists of a stack of condenser plates between which the sparks jump. The sparks mark out the path of the charged particle. See particle detector.