Radioactivity behavior in hydrothermal volcanic systems: Preliminary in situ investigations at high and low gas flux degassing areas

Long-term investigations at numerous active volcanic systems worldwide have demonstrated that environmental radionuclide measurements in volcanic plumes provide valuable insights into degassing processes, yielding important constraints on magmatic activity timescales and the depth of magmatic reservoirs. In this study, we introduce a novel methodological framework for the environmental characterization of airborne radioactivity, aimed at quantifying the coupled atmospheric transport of radionuclides and gas species (e.g., and HS) in active volcanic environments. The approach integrates in situ gamma-ray spectroscopy with geochemical measurements of air concentrations, enabling a direct comparison between radiometric signals and volcanic gas transport. The method was applied to two distinct active volcanic sites: the Pisciarelli fumarolic field (Campi Flegrei caldera, Italy), characterized by a sustained gas flux, and the Stephanos crater (Nisyros Island, Greece) where passive gas emissions are comparatively low. Gamma-ray detection acquired at multiple heights above ground (ranging from 40 to 180 cm) allowed the assessment of vertical variations in radioactivity levels and volcanic gas concentrations from both diffuse and fumarolic sources, even under very low-emission conditions. Our results show a clear coupling between concentration and gamma radiation, demonstrating that volcanic gases act as carriers of radon and its progeny, significantly modifying the vertical distribution of radioactivity. These findings provide the first direct field evidence of height-dependent radionuclide transport driven by gas fluxes and establishes a new framework for real-time environmental radioactivity monitoring in volcanic areas.