Radon concentration changes in the air of two caves in Poland

Abstract

The paper presents spatial and seasonal radon concentration changes in the air of two caves in Poland on the basis of measurements during 1995–1997. A process of seasonal radon concentration changes in the caves’ air was identified, based on research on radon occurrence in caves carried out for over 20 years. A major role in this process was ascribed to ventilation caused by atmospheric temperature changes. High radon concentrations are observed in the warm half-year (May–August), when the average air temperature exceeds the average temperature of the cave interior. Low concentrations occur, however, in the cold half-year (December– January), and a relatively sharp increase or decrease in radon concentration is related to changes in atmospheric temperatures relative to the average temperature in the cave interior. The amplitude of these radon concentration changes may reach several kBq m -3. In the Radochowska Cave the lowest monthly radon concentration (0.06 kBq m -3) was recorded in December 1996, while the highest (1.37 kBq m -3) was observed in August 1996. In the Niedźwiedzia Cave the lowest value (0.10 kBq m -3) was observed in January 1997 and the highest (4.18 kBq m -3) was noted in March 1997. The spatial variation of radon concentrations is mainly due to the morphology of the chambers and corridors of a cave, and by the distance between the measurement point and the entrance holes. As a rule, locations further from the entrance have poorer ventilation and higher radon concentrations.