Radon in dead-end caves in Europe

We report the results of 3-years of Radon-222 monitoring in six show caves across Europe, selected with the feature of having only one, or no natural entrance, defined as dead-end caves. The caves are located in Spain, Slovakia, Slovenia, and Czechia. The consecutive monitoring was performed between January 2017 and January 2020. Continuous measurements of the radon activity concentration using spectrometry detection and analysis of the α-particles of 222Rn progeny were performed. Meteorological parameters influencing gas flow were recorded inside and outside of the caves. Although the radon activity concentrations differed from one cave to another, all six of the studied caves revealed very similar trends, showing evident seasonal variability with higher values in summer and lower values in winter. The measured values of radon activity concentrations ranged between 633 and 26,785 Bq/m3. The temperature differences between the inside and outside of the caves is the main radon movements driving force. The results of this study have significant practical implications, making it possible to provide cave administrators with recommendations regarding employee or visitor time-limited access to the investigated caves. Ours is the first comparative study encompassing the most interesting dead-end caves in Europe.The authors would like to express thanks to the involved caves Administrations for the support provided during the investigation. Our work was also supported by: the Centre of Advanced Applied Sciences [CZ.02.1.01/0.0/0.0/16–019/0000778], the CzechGeo-EPOS project ‘Distributed system of permanent observatory measurements and temporary monitoring of geophysical fields in the Czech Republic’ [CZ.02.1.01/0.0/0.0/16_013/0001800], the Long-term Conceptual Development Research Organization [RVO: 67985891], the Spanish Ministry of Science, Innovation, and Universities [grant number RTI2018-099052-B-I00], the Regional Government of Comunidad Valenciana (Spain) [grant number AICO/2020/175], the Scientific Grant Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic (VEGA project no. 2/0083/18 and 2/0015/21)

Seasonal variation of radon and CO2 in the Važecká Cave, Slovakia

The continuous monitoring of 222Rn activity concentration, CO2 concentration, and microclimatologic parameters (internal air temperature and relative humidity) in the Važecká Cave (Northern Slovakia) is being carried out at three monitoring stations, namely, Gallery, Lake Hall, and Entrance Hall. Radon activity concentration and CO2 concentration exhibited a clear annual variation. The daily average of radon concentration ranged 1300–27 700 Bq/m3 at the Lake Hall station and 3600–42 200 Bq/m3 at the Gallery station. Radon reached its maximum in the summer months, from June to September. The annual maximum of CO2 concentration is registered approximately one month later than radon maximum. The annual variation of radon and CO2 is controlled by the seasonal change of ventilation regime associated with the seasonal variation of the difference between the temperature measured inside the cave and the atmospheric temperature