Caracterização química elementar e identificação de fontes de obsidianas utilizando fluorescência de raios X com equipamento portátil (PXRF)

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

26/03/2010

RESUMO

The study of archaeological and cultural heritage artifacts by means of analytical techniques with portable equipment has become increasingly routinely today. Various types of portable EDXRF equipment have been used in many different situations involving in situ analysis covering a wide range of geometries, detectors, current and voltage applied in the X-ray tubes. Therefore, it s extremely important that the geometry of the portable systems used in these studies be suitable for accurate acquisition and subsequent analysis of data. This study s main objective was to characterize the elemental chemistry of 23 samples of obsidian, 20 samples from Ecuador, 2 samples from Europe and 1 sample from Mexico and further identification of possible sources attributed to the samples. For this, the analytical sensitivity of mobile devices has been optimized using a factorial design 24 to determine elemental chemistry of archaeological objects in the laboratory and in situ, especially obsidian. For the optimization of the Portable Fluorescent X-ray Energy Dispersion (EDXRF) Systems, the variables studied were: 1 - Distance between sample and detector, 2 - Distance between sample and X-ray tube, 3 - Current applied at X-ray tube and 4 - Voltage applied at X-ray tube. The PXRF-LFNA-02 system, used for analysis of elements with atomic number greater than 26, is composed of a 4W X-ray tube (with Ag filter and target) and a Si-PIN detector model XR-100CR Ampetc Inc., which has a resolution of 221eV for the 5.9keV line (25μm-thickness Be window and Ag collimator). For the analysis of elements with atomic number lower than 26. The system used was PXRF-LFNA-03, composed of a 4W X-ray tube with W target and a Si-PIN detector, model XR - 100CR of Ampetc Inc., which has a resolution of 149eV for the 5.9keV line (12.7μm-thickness Be window and Ag collimator). It was possible to verify the presence of the main elements in the different samples analyzed obsidian, K, Ca, Ti, Mn, Fe, Rb, Sr, Y, Zr and Nb. All these elements were quantified in this work by the calibration curves, which were systematically evaluated. In general, the calibration curves were statistically significant, given the analysis of variance (ANOVA) for the ranges of concentrations set by the reference samples. The results for concentrations of K, Ca, Ti, Mn, Fe, Rb, Sr, Y, Zr and Nb are above their limits of detection (LOD) and quantification (LQ), thus having statistical significance. The results of the concentrations of certain elements for certain samples were compared with results obtained by other techniques. The comparison showed that the concentration values obtained by means of portable equipment for X-ray Fluorescence in this work are significant and can be compared without any problems with the values obtained with more robust techniques such as INAA, ICP-MS and PIXE. The optimization of device PXRF-LFNA-02 and PXRF-LFNA-03 was essential for the quality of concentration results obtained, it was possible to compare data obtained with the system PXRF-LFNA-02 optimized and not optimized and observed a significant difference values. Through cluster analysis using the concentration obtained values, it was established that are formed three main groups of samples, one formed by samples CTX1, CTX2, CTX3 and CTX4 (the region of Cotopaxi), another formed by the samples QSC1 and QSC2 (Quiscatola) and a large group formed by all the other samples. The sample of Mexico has a positive discriminant factor, which is the absence of the element Sr, which turns out to be the key element of the sample in studies of provenance and identifying sources of obsidian.

ASSUNTO(S)

física nuclear fluorescência de raio x radioatividade técnicas e aplicações nucleares nuclear physics x-ray fluorescence radioactivity

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