Seasonal variation of soil natural radioactivity in the Cosenza-Rende area, Calabria (southern Italy)

This study was carried out to determine the variations of the natural radioactivity concentration in the Cosenza-Rende urban area (southern Italy) during two seasons (winter and summer). It has been observed that spatial and temporal variability of soil gamma-ray spectra was caused by the combinate effect of geological and meteorological variations. The results indicate that the specific levels of terrestrial environmental radiation were related to the geology and litology of each area, and to the thorium (Th), uranium (U) and potassium (K) content of the bedrocks. Especially they were controlled by the occurrence of mineral such as monazite or zircon in soils. Furthermore it has been observed that there is a seasonal variability in the same sample sites which was probably related to the condition of water saturation and moisture retention. During the winter water tends to be confined in a saturated surface soil which reduces radiation permeability. Conversely during the sunny summer the soil became drier and morepermeable and the total radioactivity increases. Other causes of this seasonal variation could be temperature and atmospheric pressure variations, which, particularly during cold season, were essential due to tack effect.