Scientia Agricola (Jan 1996)
ANÁLISE QUANTITATIVA DE AMOSTRAS GEOLÓGICAS UTILIZANDO A TÉCNICA DE FLUORESCÊNCIA DE RAIOS X POR DISPERSÃO DE ENERGIA
Abstract
Este trabalho propõe uma metodologia para análise quantitativa de amostras geológicas, que apresentam uma considerável fração de elementos leves (número atômico Z ³ 13) e na radiação de excitação espalhada coerente e incoerentemente para a quantificação da fração leve da matriz (Z A quantitative analytical methodology is proposed for geological samples presenting a high fraction of light elements (atomic number less than 13), using the energy dispersive X-ray fluorescence technique with radioisotopic excitation. The proposed procedure is based on the method of the Fundamental Parameters for analytical element (Z ³ 13) evaluation, and coherent and incoherent scattered radiation for the quantitation of the light fraction of the matrix. In this method, standard samples made of pure elements and simple compounds of previously known composition and superficial density were used to estimate the relationship between the fluorescence intensity and the element concentration through elemental sensitivity and geometry factor for fluorescence. The relationship between scattered intensities and matrix light fraction was based on geometry and scattering factors as well as deferential cross sections. In order to obtain the characteristic X-rays of the elements in the Mn to Zr range a Cd-109 annular radioactive source (1.70 GBq) was used, and for Al to Cr, Fe-55 (0.74 GBq). For the X-ray detection a Si(Li) detector coupled to a multichanel emulation card was employed. The characteristic X-ray net intensity as well as the coherent and incoherent scattered intensities were obtained by using the AXIL software for spectra analysis. To test the proposed procedure, six certified samples (Soil-5/AIEA, SL-2/AIEA, SARM-2/SABS, SARM-3/SABS, SARM-4/SABS and SARM-6/SABS) were analyzed. The samples were diluted with boric acid in a 1:4 proportion to make pellets with superficial density of approximately 100 mg. cm-2.
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