The HEAO-3 high resolution gamma-ray spectrometer

Features and results produced by the HEAO 3 spacecraft gamma ray spectrometer are outlined. The instrument had high resolution germanium detectors, each 55 mm diam and 45 mm long, surrounded by a cesium iodide anticoincidence shield with four quadrants of well-crystal and a collimayor crystal. The crystals had a total effective area of 70 sq cm at 100 keV and 26.4 sq cm at .511 MeV with a spectral resolution at launch of .23 percent at 1.33 MeV. The spacecraft travels a circular orbit of 500 km altitude with an inclination of 43.6 deg. Solid methane and ammonia cryogenic fluids refrigerated the crystals for 8.5 mos, after which the shield crystals functioned as isotropic detectors for solar flare events and gamma ray bursts until mission termination in May 1981. A total of 37 solar flare type events were observed, with gamma ray events occurring with flares of class X1 or stronger.