## 4 Results and Discussion
### Radioactivity and Radon Exhalation Analysis  
A radioactivity and radon exhalation analysis was carried out not only for a more complete characterization of the shale unearthed within the investigated geological setting, but also considering that the site is quite populated throughout the year. In particular, the number of visitors varies annually based on the events held. In addition to occasional tourists, the Municipality of Tusa organizes at least two events per year at the site, each attracting approximately 50 to 60 attendees. Additionally, archaeologists from Italian-British, Palermo, and French teams conduct research at the site for a minimum of 30 days annually (62 archaeologists in 2023; 71 in 2024). Furthermore, staff from the Sicily Region--including 16 caretakers, 2 administrators, and 4 additional caretakers for holidays--are present daily. To give a quantitative idea of the impact of the site in terms of tourism, Table 3 presents data on the annual numbers of visitors to the site. It should be noted that the total number of visitors (i.e., occasional tourists) for the years 2021-2024 (up to June) is based on an estimated calculation, while the number provided for July-December 2024 is derived from the actual count of issued entrance tickets. Moreover, in 2021, the number of archaeologists reflects only the Messina and Oxford (Italian-British) and Palermo missions, as the French mission did not participate in the excavation campaign due to COVID-19. Table 4 reports the mean (averaged from the five aliquots of the analyzed rocks) activity concentrations of \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K for the investigated samples, as well as the mean specific \({}^{222}\)Rn exhalation rate. First of all, the obtained values were found to be consistent with the natural radioactive levels observed in building materials used in Italy and elsewhere [72; 73]. In particular, as far as the natural activity concentration is concerned, it is important to point out that the specific activities of \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K, for both investigated natural stones, are lower than the world average values of 35 Bq kg\({}^{-1}\), 30 Bq kg\({}^{-1}\), and 400 Bq kg\({}^{-1}\), respectively, for this environmental matrix [46], taking into account that, as also frequently described in the literature, the activity concentrations of \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K are strictly dependent on the chemical composition and mineralogical phases of the samples under study [74; 75]. In particular, the presence of muscovite (KAl\({}_{2}\)(Si\({}_{3}\)Al)O\({}_{10}\)(OH)\({}_{3}\)) in both SP1 and SP2, as determined through XRD, can be considered to represent the main radioisotope-bearing mineral present in the analyzed stones. Additional contributions may arise from plagioclase feldspars and clay minerals, which host variable amounts of potassium and trace uranium/thorium substitutions. The higher \({}^{40}\)K activity in SP2 (233 \(\pm\) 28 Bq/kg) compared to SP1 (101 \(\pm\) 13 Bq/kg) likely indicates better preservation of K-bearing phases in the outcrop. In SP1, weathering and burial processes, potentially involving leaching in a mildly acidic environment, may have induced partial dissolution of feldspars and degradation of muscovite, consistent with the \(\upmu\)-Raman and IC results. As far as the radon exhalation rate from the analyzed natural stones is concerned, it shows considerable variation, with values spreading over several orders of magnitude, although the obtained mean values closely resemble those observed worldwide [76]. In more detail, the \({}^{222}\)Rn exhalation rate was unexpectedly higher in SP1 despite its lower Ra content. This can be attributed to SPI's degraded microstructure, where increased physical disaggregation and porosity enhance radon emanation. This highlights that deterioration not only impacts the mechanical properties of lithic materials but also modifies their radiological behavior, with direct implications for site safety.