An accelerator evaluation of the performance of the Soviet-French wide-gap spark chamber for gamma-ray astronomy

Abstract A scientific model of the wide-gap spark chamber which constitutes the central part of the Soviet-French high energy gamma-ray telescope “GAMMA 1” has been exposed to a tagged gamma-ray beam at DESY, Hamburg in 1976. The main purpose of these tests was to evaluate the angular resolution achievable with this type of detector at 100 MeV. The influence on the angular resolution of the spark-chamber plate material and thickness has been investigated. The methods currently used to reconstruct the photon direction have been compared. Using only the information recorded in the first spark-chamber gap following the photon materialization plate it was found that the three-dimensional angular resolution is about 2° at 100 MeV.