engleski

Driving mechanisms and spatiotemporal variations of radon concentration in Modrič Cave (Croatia)

Emission of radon (as radioactive gas) within the karst underground appears to be a health hazard in show caves, but its origin from the deeper Earth’s crust without any surface input, makes it eligible for the reconstruction of cave ventilation patterns based on the spatiotemporal variation of its concentration. We conducted integrated measurements of radon concentrations at several locations in Modrič Cave – shallow horizontal show cave located in the foothill of Velebit Mountain (Croatia). Measurements were performed by means of passive SSNTD LR115 type II detectors (Dosirad, France) from 2018 and are still ongoing. The detectors were exposed from July to October 2018, from October 2018 to March 2019, from March to July 2019 and from October 2019 to March 2020, which covers summer-autumn, autumn-spring and spring-summer periods. The highest radon concentrations were measured in summer-autumn period and they were 2.8 ± 0.6 times (in average) higher than in the autumn-spring period. In right passage of Modrič Cave, the radon concentrations were usually higher than in the left passage and this difference was statistically significant (p=1.3·10-5, df =33) at the significance level of 0.05. Presumably, the reason is different fissure architecture of the overlying bedrock. The highest radon concentration of 10.6 ± 1.1 kBq/m3 was measured in summer-autumn period of 2018. Observed high radon concentrations during this period are indicator of poor cave ventilation caused by decreasing differences between cave and outside temperature during the late summer/early autumn. For better insight in this topic, the regular three months periods of exposure of passive detectors were established from March 2020, and, in addition, continuous radon measurements in both channels are performed by using semiconductor detector TSR3 (Tesla company, Czech Republic).

radon concentration, spatiotemporal variations, Velebit Mountain, Modrič Cave, Croatia

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