Early Results on Radioactive Background Characterization for Sanford Laboratory and DUSEL Experiments

TL;DR

This study measures and models gamma-ray and neutron backgrounds at the Homestake Mine to support low-background physics experiments, providing initial data and simulation validation for underground laboratory planning.

Contribution

It introduces a method to convert gamma-ray rates to fluxes and compares measurements with Monte Carlo simulations for different mine levels.

Findings

Measured gamma-ray fluxes agree with simulations.

Predicted neutron fluxes for various levels.

Validated simple algorithm for flux conversion.

Abstract

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 $\gamma$-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 $\gamma$-ray rates into $\gamma$-ray fluxes. A good agreement between the measured and simulated $\gamma$-ray fluxes is achieved with the knowledge of the chemical composition and radioactivity levels in the rock. The neutron fluxes and $\gamma$-ray fluxes are predicted by Monte Carlo simulations for different levels including inaccessible levels that are under construction for the planned low background experiments.