Comparação de dois métodos em espectrometria de raios gama para análise de radioatividade de baixo nível

A atividade dos elementos determinada pela espectrometria de raios gama depende do número de contagens no pico de energia da linha gama de interesse. O método convencional, que considera a área sob o pico, é comparado com uma técnica alternativa que considera o número de contagens na altura máxima do canal central do pico. A radioatividade de baixo nível deve ter precisão suficiente de acordo com as normas nacionais e internacionais, por isso métodos gráficos são utilizados na estimativa da resolução e da ordenada máxima com baixos valores de erros sistemáticos. Ambas as técnicas foram empregadas e comparadas na análise da linha gama de 1460,8keV do 40K em leite em pó usando um detector de GeHP

Energia nuclear, o que é necessário saber?

Energia nuclear consiste no uso controlado das reações nucleares para a obtenção de energia, tais núcleos, quando sofrem essa modificação, liberam uma quantidade expressiva de energia. Nos reatores nucleares, essa energia é aproveitada para gerar calor e na sequência energia elétrica pela movimentação de turbogeradores. Apesar dos grandes benefícios proporcionados pela energia nuclear para a população, ainda é um tema pouco divulgado. O objetivo deste artigo é explicar de forma simples, o princípio de funcionamento de uma usina nuclear e como, a partir da energia nuclear, obtem-se energia elétrica. As técnicas nucleares tradicionais e inovadoras são utilizadas nos mais diversos campos da atividade humana, tornando possível a realização de tarefas que por meios convencionais, hoje, seriam impossíveis de serem viabilizadas. A energia nuclear é muito utilizada na medicina, na agricultura, no meio ambiente e na indústria, principalmente, para a geração de energia elétrica. O sistema elétrico brasileiro, por ser predominantemente hídrico, é afetado profundamente pelas variações climáticas. Para que o país não dependa das condições climáticas, novas fontes de energia para geração de energia elétrica devem ser utilizadas, como no caso da energia nuclear. Em âmbito nacional, atualmente, a parcela de utilização de energia nuclear para geração de energia elétrica é apenas 4,2%. Devido ao seu baixo impacto ambiental 16% da energia elétrica total gerada no mundo advém da energia nuclear, evita-se dessa maneira, grandes quantidades de poluentes, liberados pela queima de óleo combustível ou carvão

Portable energy dispersive X-ray fluorescence for metal determination of in natura water samples

A portable EDXRF equipment was used to perform a qualitative and a quantitative in situ analysis of in natura water. Using this equipment 10 mL of water was directly analyzed. Detection limits, in mg L-1, for Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Hg and Pb were 12.5, 7.5, 4.9, 2.7, 2.8, 2.1, 1.6, 1.9, 3.4, 3.7, respectively, with deviation around 10%. In real samples, Fe, Zn and Pb were identifi ed. Given the obtained results, the analytical system performance appeared to be promising

Determination of inorganic elements in sunscreen by using energy dispersive x-ray fluorescence

Nowadays there are no official in vitro methods to determine TiO2, ZnO or other inorganic elements in sunscreen cosmetics. The objective of this work is to determine the concentration of several inorganic elements in sunscreen composition, without sample preparation, by employing a portable Energy Dispersive X-Ray Fluorescence (EDXRF) device. Particularly in the case of TiO2 and ZnO, the aim is also to estimate their Sun Protection Factor (SPF) due to the physical protection barrier. A sensitivity curve for the determination of inorganic elements in sunscreen, with atomic numbers ranging from 19 to 35, is presented. Fifteen commercial samples with different SPF from different brands were analyzed. It was determined TiO2 and ZnO concentrations with their respective SPF values, as well as to detect the presence of K, Br, Sr and Ce in the sunscreen samples by identifying and quantifying chemical elements that had not been mentioned in the formulations.Colegio de Farmacéuticos de la Provincia de Buenos Aire

WATER AND SEDIMENT ANALYSIS OF TOURISTIC PLACES IN GUARAPUAVA, PR USING A PORTABLE EDXRF SYSTEM

ABSTRACT The use of the Energy Dispersive X Ray Fluorescence (EDXRF) have increasingly been applied for in situ trace metal analysis in different kinds of samples. Results of a monitoring sampling, in the winter and summer of 2008, respectively, from 6 touristic places in Guarapuava, PR city are presented. The work consisted on the use of a portable EDXRF system constituted by a X-ray tube to excite the samples, a Si-Pin detector, a holder for the excitation-detection system and samples positioning, with the standard data acquisition electronics to register the spectra. The water samples were filtered in membranes for suspended particulate matter retention. After this, APDC precipitation methodology was applied for sample preconcentration with posterior filtering in membranes. So, the dissolved and non dissolved metal fractions were determined separately. Sediment samples were dried at 60 C for 24h and sieved through 60 mesh. Micromatter standards were used for sensitivity determination for membranes samples. For sediments 5 multi-element standards were used and calibration curves were constructed. For water membrane measurements, Fe concentration was quantified from 0.026±0.004 to 5.1±1.0, in mg L -1 . For sediments, considering all the sampling locations, Mn, Cu, Sr, Y and Nb were identified qualitatively, and it was possible to quantify the following range of elements and concentrations, mg Kg and . The performance of the equipment was very good and the results are quite satisfactory for portable equipment

Análise de água e sedimento de pontos turísticos da cidade de Guarapuava, PR por Fluorescência de Raios X com Dispersão em Energia (EDXRF)

A técnica de Fluorescência de Raios X com Dispersão em Energia (EDXRF) vem sendo muito usada para análises de metais traços em diferentes amostras ambientais. Neste trabalho são apresentados os resultados do monitoramento de seis pontos turísticos da cidade de Guarapuava (PR), no período de inverno e de verão de 2008. O trabalho consistiu no uso de um sistema portátil de EDXRF. Para as amostras de água, a concentração de Fe variou de 0.026±0.004 a 5.1±1.0, em mg L-1. Para os sedimentos, considerando todos os pontos de amostragem, foram identificados qualitativamente Mn, Cu, Sr, Y e Nb, e foi possível quantificar os seguintes elementos e faixas de concentrações, em mg kg-1: Ca (1977 – 10162), Ti (12494 – 22320), Fe (36972 – 88452), Zn (73 – 185) e Zr (158 - 960). A performance do equipamento foi muito boa e os resultados satisfatórios para equipamentos portáteis

Effect of X-ray tube configuration on measurement of key soil fertility attributes with XRF

The successful use of energy-dispersive X-ray fluorescence (ED-XRF) sensors for soil analysis requires the selection of an optimal procedure of data acquisition and a simple modelling approach. This work aimed at assessing the performance of a portable XRF (XRF) sensor set up with two different X-ray tube configurations (combinations of voltage and current) to predict nine key soil fertility attributes: (clay, organic matter (OM), cation exchange capacity (CEC), pH, base saturation (V), and extractable nutrients (P, K, Ca, and Mg). An XRF, operated at a voltage of 15 kV (and current of 23 mu A) and 35 kV (and current of 7 mu A), was used for analyzing 102 soil samples collected from two agricultural fields in Brazil. Two different XRF data analysis scenarios were used to build the predictive models: (i) 10 emission lines of 15 keV spectra (EL-15), and (ii) 12 emission lines of 35 keV spectra (EL-35). Multiple linear regressions (MLR) were used for model calibration, and the models' prediction performance was evaluated using different figures of merit. The results show that although X-ray tube configuration affected the intensity of the emission lines of the different elements detected, it did not influence the prediction accuracy of the studied key fertility attributes, suggesting that both X-ray tube configurations tested can be used for future analyses. Satisfactory predictions with residual prediction deviation (RPD) >= 1.54 and coefficient of determination (R-2) >= 0.61 were obtained for eight out of the ten studied soil fertility attributes (clay, OM, CEC, V, and extractable K, Ca, and Mg). In addition, simple MLR models with a limited number of emission lines was effective for practical soil analysis of the key soil fertility attributes (except pH and extractable P) using XRF. The simple and transparent methodology suggested also enables future researches that seek to optimize the XRF scanning time in order to speed up the XRF analysis in soil samples

Análise de metais em sangue de bovinos e no ambiente de criação de bovinos por EDXRF

O objetivo deste estudo foi identificar a presença de elementos químicos em sangue de bovinos e no ambiente ao redor das propriedades rurais em que estes animais se encontravam, localizada na Bacia do Rios das Pedras, na Serra da Esperança, município de Guarapuava – PR. A técnica analítica empregada foi a Fluorescência de Raios X por Dispersão em Energia com equipamento portátil. Foram coletadas e analisadas amostras de sangue, água, capim, sedimento e ração de três pequenas propriedades rurais. Apenas Fe foi quantificado na água apontando um local de contaminação. Potássio, Ca, Ti, Mn, Fe, Cu, Rb, Zr e Pb foram encontrados no capim. Potassio, Ca, Ti, Mn, Fe, Cu, Zn, Rb, Sr, Y, Zr, Pb foram identificados no sedimento e em uma das amostras de ração foi encontrado Pb

Assessing soil key fertility attributes using a portable X-ray fluorescence : a simple method to overcome matrix effect

The matrix effect is one of the challenges to be overcome for a successful analysis of soil samples using X-ray fluorescence (XRF) sensors. This work aimed at evaluation of a simple modeling approach consisted of Compton normalization (CN) and multivariate regressions (e.g., multiple linear regressions (MLR) and partial least squares regression (PLSR)) to overcome the soil matrix effect, and subsequently improve the prediction accuracy of key soil fertility attributes. A portable XRF was used for analyzing 102 soil samples collected from two agricultural fields with contrasting soil matrices. Using the intensity of emission lines as input, preprocessing methods included with and without the CN. Univariate regression models for the prediction of clay, cation exchange capacity (CEC), and exchangeable (ex-) K and Ca were compared with the corresponding MLR models to assess matrix effect mitigation. The MLR and PLSR models improved the prediction results of the univariate models for both preprocessing methods, proving to be promising strategies for mitigating the matrix effect. In turn, the CN also mitigated part of the matrix effect for ex-K, ex-Ca, and CEC predictions, by improving the predictive performance of these elements when used in univariate and multivariate models. The CN has not improved the prediction accuracy of clay. The prediction performances obtained using MLR and PLSR were comparable for all evaluated attributes. The combined use of CN with multivariate regressions (MLR or PLSR) achieved excellent prediction results for CEC (R-2= 0.87), ex-K (R-2 >= 0.94), and ex-Ca (R-2 >= 0.96), whereas clay predictions were comparable with and without CN (0.89 <= R-2 <= 0.92). We suggest using multivariate regressions (MLR or PLSR) combined with the CN to remove the soil matrix effects and consequently result in optimal prediction results of the studied key soil fertility attributes. The prediction performance observed for this solution showed comparable results to the approach based on the preprogrammed measurement package tested (Geo Exploration package, Bruker AXS, Madison, WI, USA)

Radioatividade natural em amostras alimentares

A medida de traços radioativos no ambiente e em alimentos é de fundamental importância para o monitoramento dos níveis de radiação a que o homem está exposto direta ou indiretamente. Este trabalho consiste na medida de traços radioativos em leite em pó, através da espectrometria gama de alta resolução. Foi possível identificar os radionuclídeos 40K, 137Cs e 232Th (obtido do 208Tl), cujas atividades foram calculadas de acordo com as normas da Agência Internacional de Energia Atômica, apresentando níveis normais para os leites analisados, podendo ser consumido sem restrições.Measurements of radioactivity traces on environment and in foodstuffs are of fundamental importance to the monitoring of radiation level to which men is exposed direct or indirectly. This work deals with the measurement of radioactivity in powdered milk samples employing high-resolution gamma-ray spectrometry technique. It was possible to identify the radionuclides 40K, 137Cs and 232Th (obtained from 208Tl), which activities were calculated according to the International Atomic Nuclear Agency rules, showing normal levels for the products analyzed, what guarantee consumption of the referent milk