Instrumental background in gamma-ray spectrometers flown in low earth orbit

Techniques are presented for calculating the instrumental continuum background in gamma-ray spectrometers flown in low earth orbit (LEO), with special attention given to simple methods developed for scaling from the better-understood measurements and calculations of background in balloon-borne instruments to LEO (Gehrels, 1985). Results are presented in the form of predictions of the background and its components for spectrometers in LEO. These predictions are compared to the measured background for the HEAO 3 gamma-ray spectrometer (Mahoney et al., 1980), and predictions are made for the International Gamma-Ray Astrophysics Laboratory mission and the Nuclear Astrophysics Explorer (Matteson et al., 1990) spectrometers. A comparison is made of various orbit options. It is shown that a critical factor is the number of times the instrument passes through the South Atlantic Anomaly (which is the region of enhanced trapped particle fluxes in LEO) and the depth of penetration on each pass.