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\bibitem{Botha_etal2019} Botha, R., Lindsay, R., Newman, R. T., Maleka, P. P., \& Chimba, G. (2019). Radon in groundwater baseline study prior to unconventional shale gas development and hydraulic fracturing in the Karoo Basin (South Africa). \textit{Applied Radiation and Isotopes}, \textit{147}, 7--13.

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