A SENSITIVE TELESCOPE FOR GAMMA RAY ASTRONOMY AT BALLOON ALTITUDES

A telescope suitable for gamma ray astronomy at balloon altitudes is described. This comprises a 42 gap spark chamber and associated event selection counters. The chamber has a sensitive area of 3000 cm2 and a conversion efficiency of 35% for 100 MeV gamma rays. The data is recorded photographically on 1.2 km of film. Two independent attitude sensing systems provide information on the orientation of the telescooe to within ± 1 2°. Provisions are included to permit the attitude to be controlled by ground command. A sensitivity for discrete sources of 5 × 10-7 photons/cm2·sec may be achieved with a flight of 8 h duration at an altitude corresponding to 3 g/cm2. © 1968.