Investigating the relationships between radon and the geology of the Sterkfontein cave

Radon, a naturally occurring radioactive gas, has become a subject of increasing interest and concern, particularly in the context of subterranean environments such as caves. This research investigates these dynamics in the Sterkfontein Cave in South Africa, which has formed in the karst geology of the Cradle of Humankind, Gauteng. Additionally, it set out to compile a radon map for the cave, identifying potential radon hotspots. Twenty-four electret ion chambers were placed in the tourist section of the cave and left for a period of 24 h. The radon concentrations were found to be between 53 Bq/m 3 and 2770 Bq/m 3 . Three regions within the cave exhibited elevated radon concentrations, with these occurrences being linked to phosphatic deposits. A subterranean lake also concentrates radon gas in the lower areas of the cave. While the cave's average radon concentration of 427 Bq/m 3 exceeds the World Health Organization's (WHO) hazardous level of 300 Bq/m 3 , occupational exposure remains minimal during a typical cave tour. Consequently, there is no discernible risk during an average tour through the cave. • TRadon concentrations were measured, interpolated, and mapped in Sterkfontein Cave, Cradle of Humankind, South Africa. • Sterkfontein Cave has yielded key palaeontological finds and has a unique geology with regions of phosphatic fill deposits. • Elevated radon levels correlated with phosphatic fill deposits, ventilation, and were observed near palaeontological areas. • The measured radon concentrations ranged from 53 Bq/m 3 to 2770 Bq/m 3 , with an average value of 427 Bq/m 3 .