## 1 Introduction
Beyond material characterization, the integration of spectroscopic data with information on the natural activity concentration of radionuclides (e.g., uranium-238 (\({}^{238}\)U), thorium-232 (\({}^{232}\)Th), and potassium-40 (\({}^{40}\)K)) is gaining increasing importance for both environmental safety and heritage conservation purposes [31; 32; 33]. Continuous monitoring of radioactivity levels is crucial to ensure compliance with radiological protection standards, especially in popular tourist destinations. In this context, the integration of the mineralogical data with activity concentration analyses offers a novel approach to conservation. This method supports the development of comprehensive preservation strategies that not only enhance the quality of restoration efforts but also ensure the safety of workers and the surrounding environment. As part of ongoing efforts to study and preserve the material heritage of _Halaesa_, this work reports the results of a comparative analysis of the mineralogical composition and radioactivity levels of two stone fragments (approx. 50 \(\times\) 30 \(\times\) 30 cm\({}^{3}\)) sampled from different areas of the ancient city of _Halaes Archonidea_. One fragment is representative of stones used in the construction of the archaeological structures (specifically the Sanctuary of Apollo at the Northern Acropolis), while the other serves as a \"reference\", having been collected from the surrounding outcrop. For this purpose, a combined approach involving \(\upmu\)-energy-dispersive X-ray fluorescence (\(\upmu\)-EDXRF) spectroscopy, \(\upmu\)-Raman spectroscopy, X-Ray Diffraction (XRD), ion chromatography (IC), High-Purity Germanium (HPGe) gamma spectrometry, and E-PERM electret ion chamber methods was adopted, with the aim of (i) obtaining insights into the stone composition at both the elemental and molecular scales, with particular regards to potential compositional variations between the two fragments due to weathering, mineral heterogeneity, and environmental exposure; (ii) assessing any degradation phenomena, including weathering agents and potential chemical contamination; and (iii) monitoring the specific activity concentrations of \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K, as well as of the mean specific \({}^{222}\)Rn exhalation rate, to assess potential radiological hazards to public health. All of the aforementioned aspects aimed to shed light on a series of open research questions, including to what extent the composition of stones used for the Sanctuary of Apollo differs from that of the surrounding outcrop materials, in order to assess whether the construction materials were locally sourced, and what are the principal weathering processes or degradation phenomena affecting the investigated fragments, to quantify any post-depositional changes that could affect their potential impact on the long-term preservation of the archaeological site. At the same time, to address any potential health and safety concerns associated with prolonged exposure to these materials in humans, especially in the context of site accessibility and conservation efforts, a monitoring of the levels of natural radioactivity and radon exhalation turned out to be crucial, thereby strengthening the interpretive framework for both archaeological analysis and radioprotection/conservation plans. It is worthy of note that the obtained results not only provide valuable data for addressing the aforementioned open questions related to the investigated archaeological record, including the understanding of the geological setting and stone-soil interactions, but also furnish a solid background for the accurate evaluation of the radiological risk associated with natural stone materials.