High Energy Astrophysics Group

HEAO-1

High Energy Astronomy Observatory-1

HEAO-1 A-4 Instrument

To cover the wide energy band of 10 keV to 10 MeV, the HEAO A-4 instrument had seven actively shielded NaI(Tl)/CsI(Na) scintillation detectors in a phoswich configuration of three types. The detector types were optimized for subintervals of this energy range: the aperture widths, detector areas and thicknesses were chosen to balance energy dependent considerations of stopping gamma-rays, minimizing background, and avoiding source confusion.

The two Low Energy Detectors (LEDs), four Medium Energy Detectors (MEDs), and the lone High Energy Detector (HED) had effective areas ranging from 40 cm² to 120 cm², with fields of view of 1.2^o x 20^o, 17o circular, and 37^o circular.

Other detectors within the instrument included seven the thick active CsI(Na) shield segments, an NE102 plastic scintillator aperture shield, and the three NE102 particle monitors. The use of a dense material with high atomic number, such as these inorganic scintillators, allowed useful detection efficiency for photons with energy up to 10 MeV, which is impossible for proportional counters at atmospheric pressures. A moveable CsI(Na) active scintillator shutter resided on top of the aperture shield and could be placed above any detector for measurement of internal background.

The active anticoincidence shield counters were used to reduce the background counting rate due to ambient charged particles and photons. The aperture shield consisted of a thin (<1 cm) sheet of plastic scintillator, sufficient to detect charged particles, but transparent to photons with energy above 10 keV.

HEAO-1 Information

Mission Objectives
Spacecraft
Hard X-ray and Low Energy Gamma-Ray Expt. (A-4)
Results
Publications