Spark Chamber System for High Energy γ‐Ray Detection

A description of an iron plate spark chamber is described. It covers ¾ of the solid angle about a liquid hydrogen target. The fifty steel plates (750×750×2 mm), separated by 3 mm, furnish a thickness of 5 radiation lengths. The voltage risetime of the plates is less than 10 nsec. The system has been used in a 250 000 picture experiment.