J. Nucl. Phy. Mat. Sci. Rad. A.

Improvements to the X-ray Spectrometer at the Aerosol Laboratory, Instituto de Fisica, UNAM

L V Mejía-Ponce, A E Hernández-López, S Reynoso-Cruces, J C Pineda, J A Mendoza-Flores, and J Miranda

KEYWORDS

X-ray fluorescence analysis, Silicon Drift Detector SDD, chemical composition of atmospheric aerosols, Standard Reference Material 2783

PUBLISHED DATE August 6, 2018
PUBLISHER The Author(s) 2018. This article is published with open access at www.chitkara.edu.in/publications.
ABSTRACT

Due to the demands of better (accurate and precise) analytical results using X-ray Fluorescence (XRF) at the Aerosol Laboratory, Instituto de Física, UNAM, it was necessary to carry out improvements in instrumentation and analytical procedures in the x-ray spectrometer located in this facility. A new turbomolecular vacuum system was installed, which allows reaching the working pressure in a shorter time. Characteristic x-rays are registered with a Silicon Drift Detector, or SDD, (8 mm thick Be window, 140 eV at 5.9 keV resolution), working directly in a high-vacuum, permitting the detection of x-rays with energies as low as 1 keV (Na Ka) and higher counting rates than in the past. Due to the interference produced by the Rh L x-rays emitted by the tube normally used for atmospheric and food analysis with Cl K x-rays, another tube with a W anode was mounted in the spectrometer to avoid this interference, with the possibility to select operation with any of these tubes. Examples of applications in atmospheric aerosols and other samples are presented, to demonstrate the enhanced function of the spectrometer. Other future modifications are also explained.

INTRODUCTION

The fast advance of science in certain fields requires frequently the knowledge of the chemical composition of samples. In particular, the determination of trace elements concentrations needs sensitive and non-destructive analytical methods, such as spectrometric techniques. These scientific disciplines include materials science, agriculture, art, medicine, biology, archaeology, geology, and environmental sciences [1]. Among the spectrometric techniques, those based on x-rays as the secondary radiation, are especially important [2]. The most common are X-Ray Fluorescence (XRF), Electron Probe Microanalysis (EPMA), Particle Induced X-ray Emission (PIXE), and Extended X-ray Absorption Fine Structure (EXAFS). Specifically, XRF can be based on the use of different primary radiation emitters (like radioactive sources, x-ray tubes, or synchrotron light). Recently, a multipurpose x-ray spectrometer was developed, mainly for the analysis of environmental samples [3]. It has been applied in several studies, focused on air pollution studies [4] and food chemistry [5]. In these works, several issues were identified, which limited the results obtained with the XRF analysis. Therefore, several improvements to the operation of the x-ray spectrometer were carried out, in order to be obtain more accurate, precise, and sensitive results with XRF. In the present work, the upgrades, aimed to detect lighter elements x-rays than before, eliminate peak interferences, and faster vacuum conditions, are detailed.

Page(s) 57-60
URL http://dspace.chitkara.edu.in/jspui/bitstream/123456789/739/1/09_JNP.pdf
ISSN Print : 2321-8649, Online : 2321-9289
DOI 10.15415/jnp.2018.61009
CONCLUSION

The improvements carried out in the x-ray fluorescence spectrometer provide much better results, both from the accuracy and precision (uncertainty) points of view. The possibility to reach vacuum conditions in a shorter time also increased the operating productivity during routine analyses, which are important when a large number of samples must be irradiated. The use of different x-ray tubes prevents the interference with lines of important elements (Si, S, and Cl, for instance). Finally, the detection of light elements (Na, Mg, Al) with reasonable high efficiencies represents an important advance in the characterization of environmental and food samples.

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