Caracterização de solos pouco desenvolvidos com foco na fluorescência de raios x e parâmetros de interação da radiação

Abstract

Due to the accelerated world population growth, increasing pressure on environmental preservation areas has become common, aiming at activities such as mining and agricultural exploitation. This has caused drastic changes in the landscapes with negative consequences that has been affected the planet’s climate. Generally, in the physics field applied to soils, conventional techniques are used to the soil characterization. However, there are other nonconventional techniques that can be employed based on the X-ray and gamma ray interaction with the matter. Techniques such as gamma ray attenuation have been used successfully for many decades in the study of properties such as soil density and moisture based on the attenuation coefficient parameter. Although, there is still other radiation interaction parameters that can be explored aiming the soil characterization. Brazil has a great area been used in the agriculture and also areas belonging to forest reserves, whose objective is to protect the natural biomes. Many of these areas are located on poorly developed (weathering soils) soils, such as Cambisols and Entisols. In this way, characterizing this type of soils has become vital because of its great importance in the environmental point of view. In the scientific literature, there is no report of studies that approach the radiation attenuation properties in soils of conservation units (protected of human action theoretically). Besides this, practically there is no study of the radiation attenuation properties of young soils such as Entisols that are in the formation phase, known for their sandy texture, absence of a diagnostic horizon and presence of the material from the original rock and with hard weathering minerals. This thesis study is based on the following hypothesis: 1) radiation interaction parameters present variation even when the chemical composition of the soil does not present significant differences; 2) different uses of the soils change its chemical composition and affect the radiation interaction parameters, in a way that this cannot be consider static even for the same type of soil; 3) young soil and poorly developed (absence of well-defined horizons) shows differences in the soil chemical composition and in the radiation interaction parameters along the soil profile; 4) the radiation interaction parameters can be used in the characterization of the soil, mostly in those not submit to human intervention; and 5) changes in the chemical analysis of the soil affect the calculation of the radiation interaction parameters. This thesis study is based on two studies. The objective of the first was to analyze the radiation interaction parameters of different horizons (A: 0-13, AB: 13-30, Bi: 30-80, C: 80-127 cm) of a Cambisol, located in the conservation unit of the Serra Dourada State Park (PESD). For the conduction of this study the oxide composition was obtained by two methods (X ray fluorescence by energy dispersion – EDXRF and by wavelength dispersion - WDXRF), in order to compare this obtained results. The mass attenuation coefficient (μ/ρ) was obtained through the computational simulation using the XCOM, GEANT4 and Fluka program. Based on the μ/ρ data the other radiation interaction parameters where calculated: the molecular (σM), atomic (σA), electronic cross sections (σE), effective atomic number (Zeff) and electronic density (Nel). The results indicate that both elemental analysis techniques are effective in the oxide detection; however, the WDXRF showed more sensibility. In the second study, the WDXRF method was employed in the characterization of a Quartzarenic Entisol of an agriculture familiar settlement located in the Oriental Amazon. The studied soils was submit to two uses system (Pasto and Roça de Toco), being a forest area used as reference. The study was conducted in a soil profile in the layers of 0-5, 5-10, 10- 20 e 20-40 cm. The results obtained with both soils (Cambisol and Entisol) made possible new insights about how the oxide content affect the radiation interaction parameters, given that this parameters where sensitive to the chemical soil composition. Still, it was possible an analysis of how the values of the mass attenuation coefficient are influenced the computational simulation such as the ones based on the Monte Carlo (GEANT4 and Fluka) and the mixture rule (XCOM). The Cambisol results can be a reference for posterior studies, in soils with the same classification and located in regions next to the PESD, in a way to verify how human actions can affect this type of soil. The results obtained for the Entisol highlight that the uses affected the oxide soil composition, mostly in oxides related to the secondary minerals (Al2O3, Fe2O3 e TiO2). Such fact highlights how human actions can affect soil properties that reflect in his radiation interactions parameters with the matter. Finally, the obtained results for both soils showed that the interaction parameters, in combination with the elemental analysis, serve as base for a soil characterization. Generally, such measurements are made with base in properties related to the soil structure, and in this study, was proposed the use of techniques that employed deformed samples, that is, obtained after the structure has been broken.