Background model for a gamma-ray satellite on a low-Earth orbit.

The main background components in a low-Earth orbit are charged particles and photons, both primary and secondary, as well as neutrons. A model of these components, based on data from previous instruments, has been developed for energies between 10 keV and 100 GeV. The model dependence on inclination has been studied for a mean solar activity and activation simulations from such a background have been carried out using the model of a possible future gamma-ray mission (e-ASTROGAM). The results from these simulations have been compared with the activation from the passage through the South Atlantic Anomaly (SAA). The primary protons are found to be the main contributor of the activation at 0^o while the long-term activation from the passage through the SAA becomes the main source of background for inclinations higher than ∼10^o. The SAA contribution to the 511 keV line background must be always taken into consideration, up to several minutes after the passage for high inclination orbits (igtrsim15 ^o).