Soils subjected to disaggregation can break into aggregates of different sizes composed of sand, clay, and silt particles. Each aggregate contains different oxides, which can vary according to the aggregate size and influence its properties, such as the radiation interaction parameters. These parameters are relevant in the evaluation of radiation shielding and soil physical properties. Thirteen tropical/subtropical soils of contrasting textures (clayey and loamy/sandy) with two aggregate sizes (2-1 mm and <45 μm) were studied. The radiation parameters analyzed were the atomic (σA), electronic (σE), and molecular (σM) cross-sections; the effective atomic number (Zeff); and the electron density (Nel). We verified that the aggregate sizes affected the major oxides (SiO2, Al2O3, Fe2O3). In general, the attenuation coefficient and Zeff were sensitive to the clayey soils' aggregate sizes (low photon energies). However, the loamy/sandy soils did not exhibit differences among the parameters. As the photon energy increased, only Zeff presented differences for most soils. We also verified that σM, Zeff, and Nel were the most sensitive parameters to the soil composition. Although the soil chemical composition was influenced by the studied aggregate sizes, the radiation parameters exhibited differences for only some of these parameters. This means that the aggregate size is practically irrelevant when radiation parameters are determined based on X-ray fluorescence.
Keywords: effective atomic number; electronic cross-section; mass attenuation coefficient; soil chemical composition; soil granulometric fractions; soil microaggregates.