Natural radioactivity distribution and soil properties: a case study in southern Italy 1 Ilaria Guagliardi, Nicola Ricca, Maria Grazia Cipriani, Donatella Civitelli, Raffaele Froio, Anna Lia Gabriele, Gabriele Buttafuoco National Research Council of Italy - Institute for Agricultural and Forest Systems in the Mediterranean (ISAFOM), Via Cavour 4-6, Rende - Cosenza (Italy) ilaria.guagliardi@isafom-cnr.it Rosanna De Rosa Department of Earth Sciences, University of Calabria, Ponte Pietro Bucci, 87036 Arcavacata di Rende - Cosenza (Italy) Abstract: Mapping environmental radioactivity from field gamma-ray spectrometry is a valuable tool for understanding and interpreting pedological control of naturally occurring radioactivity. Soil properties and water content affect the behaviour of natural radioactivity. The main aim of the study were to explore and map the activity of three naturally occurring radionuclides ( 232 Th, 238 U, 40 K) in an olive orchard and investigate the relationship between some soil properties and the activity of the three radionuclides. Keywords: natural radioactivity, soil, water content, grain size 1. Introduction Environmental natural radioactivity in the soil is due to the decay of radionuclides derived from minerals in the earth’s crust. Many naturally occurring elements have radioactive isotopes, but only potassium, and the uranium and thorium decay series have radioisotopes producing gamma rays of sufficient energy and intensity to be measured by gamma ray spectroscopy (IAEA, 2003). The radioactive isotope of potassium 40 K occurs as a fixed proportion of K in the natural environment and these gamma rays can be used to estimate the total amount of K present. Uranium and thorium occurs naturally as the radioisotopes 238 U, 235 U and 232 Th. Neither 238 U nor 232 Th emit gamma rays and their concentrations are estimate from their radioactive daughter products and reported as equivalent uranium (eU) and equivalent thorium (eTh). The mineral composition of the parent material controls the natural radioactivity of soils (Navas et al., 2011) and the processes of weathering, sedimentation, leaching and sorption, and the movement of groundwater may influence activity levels of natural radionuclides (Dowdall and O’Dea, 2002). Soils play a major role in the cycling of radionuclides and their physico-chemical properties influence the mobility and bioavailability of these radionuclides in terrestrial ecosystems (Kabata- Pendias and Pendias, 2001). A fundamental characteristic of the soil, which greatly influences the environmental transport of radioactivity, is the distribution by grain size. Approximately 95% of the measurable gamma radiation is emitted from the upper 0.5 meters of the profile (Gregory and Horwood, 1961) and the value of gamma spectroscopy lies principally in the amount of radioisotopes of K, U and Th contained in rocks and soil profiles (Dickson and Scott, 1997). Signal attenuation of radioactivity increases by approximately 1% for each 1% increase in volumetric soil water content (Cook et al., 1996). 1 This research was funded by the Action 2 – Public research laboratory mission oriented. APQ – Scientific Research and technological Innovation in Calabria Region. Laboratory for Food Quality, Safety, and Origin (QUASIORA).