Vidicon Spark Chamber Detector for Gamma-Ray Astronomy

A small, relatively low-power spark chamber with vidicon readout has been developed for balloon-and satelliteborne high-energy gamma-ray astronomy investigations. The system has been extensively ground tested, and is scheduled for a balloon launch in winter 1965. The spark chamber consists of eight 7" × 7" × 1/8" and fifteen 7" × 7" × 0.02" aluminum plates for determination of gamma-ray flux arrival, direction, and interaction mean free path. Beneath the spark chamber, a lead-glass ¿erenkov counter, 10 radiation lengths thick, is employed as an energy calorimeter. The spark chamber detector continually views a solid angle of 0.84 steradian, and can determine photon arrival direction to a few degrees. A stereo view of the spark chamber event along with a pulse height display (512 channels) from the Nerenkov counter is recorded on the cathode of a conventional vidicon. The vidicon is scanned at the normal 30 cycle/sec rate and, when balloon-flown, is telemetered to a mobile ground station via a 7-watt transmitter, with a range of approximately 350 miles. The video signal is stored both on video tape and on kinescope film. Visual display allows positive identification of gamma-ray events. The system has been assembled and tested on the ground with satisfactory results. Several systems for automatic computer data reduction using the video tape have been considered and are discussed.