A ESPECTROMETRIA DE RAIOS GAMA NA CARACTERIZAÇÃO DE FÓSSEIS E ARTEFATOS ETNOARQUEOLÓGICOS

Abstract

Gamma-ray spectrometry (GRS) is a widely utilized nuclear physics technique across various sectors, including nuclear industry, geology, and astrophysics. It enables the measurement of concentrations of radionuclides from the 238U and 232Th series, as well as the radionuclide 40K, providing valuable insights into mineralogy, geological processes, and formation environment. However, its applicability in studies involving samples where crushing and homogenization are not feasible is limited due to geometric adequacy issues. Nevertheless, GRS technique, when employed without strict control of measurement geometry, can unveil intriguing sample characteristics, particularly when analyzing concentration ratios among different radionuclides of the 238U and 232Th series and the radionuclide 40K, a procedure that mitigates geometry's influence on results. This paper presents three studies examining the potentials and limitations of gamma-ray spectrometry technique applied to the investigation of objects with diverse geometries. To explore the influence of geometry on measurements conducted by GRS technique and assess the possibility of determining concentration ratios of natural radionuclides (Th/U, Th/K, and K/U) in samples with different geometries, measurements were carried out on a sample enriched with higher than natural content of thorium, uranium, and potassium. The sample was packed into nine cylinders, each weighing 30 grams. Measurements were taken both on the top and the side of the detector, reproducing and varying distinct geometric shapes in each measurement. The spectral analysis methodology followed the International Atomic Energy Agency (IAEA) recommendations for U, Th, and K analysis in rocks, soils, and sediments, followed by simple calculation of concentration ratios. The results demonstrated that gamma-ray spectrometry technique is a viable alternative for analyzing samples with different geometries, provided it is performed with equivalent elemental ratios of eTh and eU, determined by the nuclides 212Pb (238.63 keV), 214Pb (351.93 keV), 214Bi (1764.49 keV), 208Tl (2614.51 keV), and 40K (1460.82 keV). Following the same methodology, 32 fossil samples from the Museum of Natural Sciences of Guarapuava were also analyzed, along with 11 ceramic samples and 4 clay samples from three Quilombola communities in three municipalities in the state of Maranhão. In the case of fossils, the interpreted GRS data provided insights into diagenetic processes (mineralization) and the redox conditions of the sedimentary environment in which they were formed. Thus, the feasibility of characterizing fossil samples with irregular geometries and varied densities using gamma-ray spectrometry was demonstrated. For ceramic and clay samples, an experimental archaeology study was conducted, testing the hypothesis of the technique's efficiency in separating previously known distinct samples. In addition to the GRS technique, energy-dispersive X-ray fluorescence (EDXRF) technique was also tested, both coupled with multivariate statistical tools. The results of both techniques revealed the existence of three sample groups, as expected. Furthermore, additional sample information was indicated, such as the type of clay mineral and redox potential. These findings suggest that the GRS technique can be utilized in research related to archaeological and paleontological samples, as well as other cultural heritage samples, where preservation of their integrity is of vital importance.