# The Relationship between Radon and Geology: Sources, Transport and Indoor Accumulation
## 2 The Origin of Radon
### Accumulation of Radon in Indoor Environments
#### 2.3.6 Rn Accumulation
It provided crucial insights into seasonal variability and spatial differences in radon concentrations. This study paved the way for more pragmatic applications of radon monitoring, providing crucial data for cave administrators and agencies regulating cave access. The study by [PERSON] et al. (2018) returned to Altamira Cave, utilising radon as an atmospheric tracer over a 30-year span [134]. This research demonstrated the utility of radon in revealing information about gaseous exchanges inside caves and with the external environment. The study noted how changes, such as the installation of a second closure, drastically reduced the connection between cave chambers, indicating the long-term impact of human intervention on cave environments. Most recently, [PERSON] et al. (2022) examined the radon concentration dynamics in La Cueva del Viento, a volcanic lava tube in Tenerife Island [135]. The study found that rain and external air temperature significantly influenced the seasonal and daily variations in indoor radon concentrations. Importantly, this research determined the annual effective doses received by guides and visitors to be safe. However, it also recommended classifying La Cueva del Viento as a \"Monitoring zone\" requiring a regular monitoring program, pointing to the need for continuous monitoring and vigilance to ensure safety. Of particular interest is the Castanar de Ibor cave in Spain, a subterranean karst system with distinct characteristics, which presents extraordinarily high levels of radon gas concentration. [PERSON] et al. (2009) provides a baseline understanding of the cave's microclimate, noting its stability and sensitivity to environmental changes [136]. The study emphasizes the cave's high and consistent radon content (average value of 32,200 Bq\(\cdot\)m\({}^{-3}\)) that varies in response to meteorological conditions, barometric fluxes, and anthropogenic influences such as uncontrolled cave entrance openings. A closer examination of the radon levels by [PERSON] et al. (2006) revealed an annual average of 32,246 Bq\(\cdot\)m\({}^{-3}\) with a peak reaching 50,462 Bq\(\cdot\)m\({}^{-3}\) in April 2005 [137]. The research suggests that the radon concentration variations are primarily driven by differences in internal and external temperatures. To mitigate the associated radiation risks, time-limited visits and pre-visit ventilation measures were introduced, leading to a 10-12% reduction in radon levels during visits. [PERSON] et al. (2011) further elaborates on the interplay between cave and external conditions, highlighting two microclimatic patterns: trace gas storage in the cold-wet season and CO\({}_{2}\) emissions during the warm-dry season [138]. The research underlines the role of climatic factors such as temperature differentials, cave air pressure, rainfall, and anthropogenic factors in influencing gas concentrations within the cave. In the most recent study, [PERSON] et al. (2015) confirmed the high radon concentration, noting a seasonal pattern of summer minimums and fall maximums [139]. The study posits that reductions in air-filled porosity in soil and rock due to condensation or rainfall could be responsible for this seasonal trend. In terms of safety measures, the study proposes adjustments to touristic paths according to radon concentration distribution. Collectively, these studies contribute to a nuanced understanding of the Castanar de lbor cave's microclimate and its high radon levels, pointing to the need for effective management strategies to balance tourism interests with health and safety concerns. These studies also contribute valuable information which complements the lists provided by [PERSON] (2005) and [PERSON] et al. (2023).