Spark Chamber for Gamma‐Ray Astronomy

A spark chamber system is described which is designed to detect γ rays in the cosmic radiation on high altitude balloon flights. It has (1) an acceptance cone of 30° half angle; (2) time resolution of 150 msec; (3) energy resolution from 30 to 500 MeV; and for a 100 MeV γ ray, (4) a conversion efficiency of 12.4%, and (5) angular resolution of 3°. Events are recorded photographically. The system is triggered by a large scintillator above the chamber in anticoincidence with a scintillator‐Čerenkov telescope beneath. Only the chamber and high voltage components are pressurized. A magnetometer direction monitor locates the γ ray direction to ±3° in right ascension and declination. The system has operated successfully on day and night flights and has a total weight of 80 kg.