Gamma-ray Flux at Different Levels in the Homestake Mine Measured with NaI detectors

Characterization of various backgrounds is an important step to the design of DUSEL in which the low background experiments are being planned. The gamma-ray flux at the different levels in the Homestake has been measured using three identical NaI detectors arranged as an array. We report the gamma-ray flux in four categories: 1) below 3 MeV, the spectrum is expected to be dominated by radioactivities from the rocks; 2) between 3 and 5.5 MeV, the shape of the spectrum should be well explained by U, Th and daughters, which are internal contamination in the NaI crystals; 3) between 5.5 to 10 MeV, the gamma-rays flux is dominated by neutron capture on surrounding materials; and 4) the gamma-ray flux above 10 MeV is induced by muon bremsstrahlung. The measured flux will be compared to the prediction by the Monte Carlo simulation.