Research and Characterization of Laboratory Dual Dispersions and Dural Focuses X-Ray Fluorescence Spectrometer Instrument Development
SHEN Ya-ting1, 2, HAN Ling-yun1, 3, CHEN Jun-ru1, 3, GUO Rong1, ZHU Shuai1, 2, LI Ying-chun1, MA Sheng-feng1, ZHU Yun1, ZHANG Bao-ke1, LUO Li-qiang1*
1. National Research Centre of Geoanalysis, Beijing 100037, China
2. Key Laboratory of Eco-geochemistry, Ministry of Natural Resources, Beijing 100037, China
3. China University of Geosciences (Beijing), Beijing 100083, China
Abstract：X-ray emission spectroscopy is an in situ non-destructive method to obtain chemical species of elements, and the development of laboratory-type XES devices worldwide is still in the exploratory stage. Energy-Dispersive X-Ray Fluorescence Spectrometer (EDXRF) and Wavelength-Dispersive X-Ray Fluorescence Spectrometer (WDXRF) are widely used in geological, environmental and archaeological fields. However, although EDXRF has a simple structure and can realize rapid, non-destructive detection of multiple elements, the resolution is not ideal, the spectral line interference is serious, and the detection limit is poor. Although WDXRF can distinguish most elements with spectral overlapping characteristics in conventional applications, the structure and cost are complicated. To explore the development of laboratory-type XES devices, this study synthesizes the performance advantages of the Dual Dispersions and Dural Focuses X-Ray Spectrometer (DDF-XRS) design concept and successfully develops the principle prototype. The experimental data and analysis results show that this DDF-XRS spectrometer combines the advantages of both micro EDXRF and WDXRF with a simple structure, good signal-to-noise ratio, high resolution, and low detection limit characteristics. Through the wavelength-energy double dispersion technology, X-rays are firstly diffracted by the crystal to undergo wavelength dispersion, thus obtaining monochromatic light, and at the same time, the energy dispersion of the silicon drift detector can be used to observe the degree of monochromaticity, reduce the risk of misjudgment of spectral line interference, and improve the accuracy and reliability of the analysis results, which overcomes the limitations of the complex structure for WDXRF and the insufficient energy resolution of the EDXRF, and highlights the necessity and superiority of the double dispersion. This technology overcomes the limitations of WDXRF multi-element peak determination and EDXRF energy resolution, emphasizing the necessity and superiority of double dispersion. At present, the resolution of the DDF-XRS spectrometer is 45 eV, which can reduce the spectral line overlap of transition metal Kβ to Kα peaks; at the same time, it significantly reduces the background of the continuum spectrum, and the optimal signal-to-noise ratio is >1 000; and the detection limit of Cr in the determination of geologic samples can be up to 0.26 mg·kg-1. With the application of DDF-XRS, the transition metal Kα1 and Kα2 spectral lines can be resolved to a certain extent, and it is expected that the resolution can be further improved by combining with linear or two-dimensional array detectors to realize the determination of X-ray emission fingerprint spectra to obtain the chemical forms of the analyzed elements. Since the current crystal properties cannot fully resolve the overlapping spectral lines of transition metals, the search for curved crystals with high fractionation capacity and diffraction intensity will be the next research focus.
Key words：X-ray fluorescence; Bent crystal; Curved crystal; Resolution; Detection limit; Wavelength dispersion; Energy dispersion
