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)