Abstract
The Third High Energy Astronomy Observatory (HEAO 3), successfully launched into low earth orbit on 20 September 1979, carries a large high resolution gamma-ray spectrometer designed for cosmic nuclear spectroscopy. This Gamma-Ray Spectrometer (the HEAO C-1 experiment) consists of a cluster of four coaxial high purity germanium detectors, each with a volume of approximately 100 cm3. Surrounding the germanium detectors is a 6.6 cm thick CsI shield operating in active anticoincidence with the central detectors and defining a field of view of about 30° fwhm. An initial energy resolution of 3 keV fwhm at 1.46 MeV was achieved for each detector. All valid events in the germanium detectors are individually analyzed by an 8192 channel pulse area analyzer and transmitted at a maximum rate of 15.6 events/s for each detector. During a 6 month mission, the experiment will perform a complete sky survey for narrow cosmic gamma-ray line emission to the sensitivity level of about 10−4 photons/cm2 s over an operating energy range of 0.05–10 MeV.