  Sharjah-Sat-1 is a 3U cubesat with a CdZnTe based hard X-ray detector, called
iXRD (improved X-ray Detector) as a scientific payload with the primary
objective of monitoring bright X-ray sources in the galaxy. We investigated the
effects of the in-orbit background radiation on the iXRD based on Geant4
simulations. Several background components were included in the simulations
such as the cosmic diffuse gamma-rays, galactic cosmic rays (protons and alpha
particles), trapped protons and electrons, and albedo radiation arising from
the upper layer of the atmosphere. The most dominant component is the albedo
photon radiation which contributes at low and high energies alike in the
instrument energy range of 20 keV - 200 keV. On the other hand, the cosmic
diffuse gamma-ray contribution is the strongest between 20 keV and 60 keV in
which most of the astrophysics source flux is expected. The third effective
component is the galactic cosmic protons. The radiation due to the trapped
particles, the albedo neutrons, and the cosmic alpha particles are negligible
when the polar regions and the South Atlantic Anomaly region are excluded in
the analysis. The total background count rates are ~0.36 and ~0.85 counts/s for
the energy bands of 20 - 60 keV and 20 - 200 keV, respectively. We performed
charge transportation simulations to determine the spectral response of the
iXRD and used it in sensitivity calculations as well. The simulation framework
was validated with experimental studies. The estimated sensitivity of 180 mCrab
between the energy band of 20 keV - 100 keV indicates that the iXRD could
achieve its scientific goals.
