Simulations and measurements of the background encountered by a high-altitude balloon-borne experiment for hard X-ray astronomy

We have modelled the hard X-ray background expected for a high-altitude balloon flight of the Energetic X-ray Imaging Telescope Experiment (EXITE2), an imaging phoswich detector/telescope for the 20-600 keV energy range. Photon- and neutron-induced contributions to the background are considered. We describe the code and the results of a series of simulations with different shielding configurations. The simulated hard X-ray background for the actual flight configuration agrees reasonably well (within a factor of similar to 2) with the results measured on the first flight of EXITE2 from Palestine, Texas. The measured background flux at 100 keV is similar to 4 x 10(-4) counts cm(-2) s(-1) keV(-1).