Radon Monitoring and Early Low Background Counting at the Sanford Underground Laboratory

Radon detectors have been deployed underground at the Sanford Underground Laboratory at the site of the former Homestake Mine in Lead, SD. Currently, no radon mitigation measures are in place in the underground environment, and the continuing evolution of the facility ventilation systems has led to significant variations in early airborne radon concentrations. The average radon concentration measured near the primary ventilation intake for the 4850-ft level (Yates shaft) is 391 Bq/m3, based on approximately 146 days of data. The corresponding average radon concentration near the other main ventilation intake for the 4850-ft level (Ross shaft) is 440 Bq/m3 based on approximately 350 days of data. Measurements have also been collected near the 1250-ft level Ross shaft, with average radon concentrations at 180 Bq/m3. Secondary factors that may increase the baseline radon level underground include the presence of iron oxide and moisture, which are known to enhance radon emanation. The results of the current radon monitoring program will be used for the planning of future measurements and any potential optimization of ventilation parameters for the reduction of radon in relevant areas underground.