  SABRE (Sodium-iodide with Active Background REjection) is a direct dark
matter search experiment based on an array of radio-pure NaI(Tl) crystals
surrounded by a liquid scintillator veto. Twin SABRE experiments in the
Northern and Southern Hemispheres will differentiate a dark matter signal from
seasonal and local effects. The experiment is currently in a Proof-of-Principle
(PoP) phase, whose goal is to demonstrate that the background rate is low
enough to carry out an independent search for a dark matter signal, with
sufficient sensitivity to confirm or refute the DAMA result during the
following full-scale experimental phase. The impact of background radiation
from the detector materials and the experimental site needs to be carefully
investigated, including both intrinsic and cosmogenically activated
radioactivity. Based on the best knowledge of the most relevant sources of
background, we have performed a detailed Monte Carlo study evaluating the
expected background in the dark matter search spectral region. The simulation
model described in this paper guides the design of the full-scale experiment
and will be fundamental for the interpretation of the measured background and
hence for the extraction of a possible dark matter signal.
