Abstract
Ensuring high air quality in the atmosphere of Zhijindong Cave is essential, for it is one of the most scenic in Asia and has received millions of tourists each year. Radon, as the most important radioactive carcinogen, is a priority and has been measured since just after its opening. However, an artificial exit was opened in 2002, and it is still unclear what the influence of that has been on the radon concentration in the cave atmosphere. In this study, we use RAD7 to monitor the spatiotemporal variations of radon concentration in the atmosphere of Zhijindong Cave for a whole year. The results show that radon concentration is generally higher in the hot season and lower in the cold season, and both with a distinct spatial differences. The highest measured radon concentration is 1691 Bq/m3, which is lower compared with the previous study. The reduced radon concentration could be caused by the strengthened cave ventilation due to the artificial exit. The temporal variation of radon concentration is related to the outside temperature change, while the spatial variation is mostly related to the different cave layers. The effective dose is negligible for tourists, but can be as high as 9.7 mSv for tour guides and 22.6 mSv for photographers.
Highlights
Radon (222Rn) is the decay product of radium (226Ra) in the uranium (238U) decay chain
The overall annual average radon concentration is 509 Bq/m3, and the highest value is 1692 Bq/m3, which is lower than the highest radon concentration measured in Zhijindong Cave (2191 Bq/m3) by an earlier study [27]
The overall annual average radon concentration in Zhijindong Cave is higher than 300 Bq/m3 recommended by International Commission on Radiological Protection (ICRP) for indoor environment and lower than 1000 Bq/m3 for working environment [34], but the radon concentration during hot seasons in many scenic spots is higher than 1000 Bq/m3, so there will be potential health risk if one stays for a long time in Zhijindong Cave
Summary
Radon (222Rn) is the decay product of radium (226Ra) in the uranium (238U) decay chain. It is a colorless and tasteless radioactive gas with a half-life of 3.8 days. Radon in the natural environment mainly comes from the release of rock and soil, and the concentration difference is obvious in different regions (different background values of uranium and radium) and different environments (outdoor, basement, indoor, cave, and mine). Radon concentration in the open atmosphere generally ranges from a few Bq/m3 to more than a dozen Bq/m3 [5,6], while in indoors and basements can reach thousands of Bq/m3 [7]. Radon concentrations can reach hundreds of thousands of Bq/m3 in some cave environments [8,9]. The cave ventilation caused by meteorological conditions is considered to be the biggest influencing factor [9]
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