Effects of source rocks, soil features and climate on natural gamma radioactivity in the Crati valley (Calabria, southern Italy)

The potential relationships among radionuclides, source lithologies, soils and seasonal climate regimes represents an innovative scientific strategy to approach the study of natural radioactivity in terms of spatial and temporal variability. In this study, a total of 181 sites were measured for 238U, 232Th 40K and total radioactivity activities, by means of high-resolution ?-ray spectrometry, from different bedrocks and soils of an urban and peri-urban area of the Calabria region, southern Italy. The pilot district of Cosenza and Rende municipalities, located in the Crati valley, can be considered as representative of much wider Mediterranean areas for its common geological, geomorphological, pedological, climatic and urbanization characteristics, as well as for the widespread presence of rocks hosting radionuclides. In addition, selected rocks samples were collected and analysed, using SEM-EDS and XRPD techniques, to assess the main sources of radionuclides. The gamma-natural background is intimately related to differing petrologic features of crystalline source rocks and sediments and to peculiar pedogenetic features and processes. The radioactivity survey was conducted during two different seasons with marked changes in the main climatic parameters, namely dry summer and moist winter, to evaluate possible effects of seasonal climatic variations and soil features on radioactivity measurements. Seasonal variations of radionuclides activities show their peak values in summer. The activities of 238U, 232Th and 40K exhibit a positive correlation with the air temperature and are negatively correlated with precipitations.