  The different background components in a low-Earth orbit have been modeled in
the 10 keV to 100 GeV energy range. The model is based on data from previous
instruments and it considers both primary and secondary particles, charged
particles, neutrons and photons. The necessary corrections to consider the
geomagnetic cutoff are applied to calculate the flux at different inclinations
and altitudes for a mean solar activity. Activation simulations from such a
background have been carried out using the model of a possible future gamma-ray
mission (e-ASTROGAM). The event rates and spectra from these simulations were
then compared to those from the isotopes created by the particles present in
the South Atlantic Anomaly (SAA). The primary protons are found to be the main
contributor of the activation, while the contributions of the neutrons, and
that of the secondary protons can be considered negligible. The long-term
activation from the passage through the SAA becomes the main source of
background at high inclination (i$\gtrsim10^\circ$). The used models have been
collected in a Python class openly available on github.
