Early results on radioactive background characterization for Sanford Laboratory and DUSEL experiments

Measuring external sources of background for a deep underground laboratory at the Homestake Mine is an important step for the planned low-background experiments. The naturally occurring γ-ray fluxes at different levels in the Homestake Mine are studied using NaI detectors and Monte Carlo simulations. A simple algorithm is developed to convert the measured γ-ray rates into γ-ray fluxes. A good agreement between the measured and simulated γ-ray fluxes is achieved with the knowledge of the chemical composition and radioactivity levels in the rock. The neutron fluxes and γ-ray fluxes are predicted by Monte Carlo simulations for different levels including inaccessible levels that are under construction for the planned low-background experiments.