双色散-双聚焦X射线光谱仪研制与特性研究

Research and Characterization of Laboratory Dual Dispersions and Dural Focuses X-Ray Fluorescence Spectrometer Instrument Development

X射线发射谱技术(XES)是一种原位无损获得元素化学形态的技术方法,目前国内外实验室型X射线发射谱测定装置的研制尚处于探索阶段。能量色散X射线荧光(EDXRF)光谱仪和波长色散X射线荧光(WDXRF)光谱仪在地质、环境、考古等多学科领域得到广泛应用,然而,EDXRF虽结构简单,可实现多元素快速无损检测,但分辨率不理想、谱线干扰严重,检出限较差;WDXRF虽可分辨常规应用中多数具有谱线重叠特性的元素,但结构复杂成本高。为探索实验室型XES装置研制,该研究综合了能量色散X射线荧光和波长色散X射线荧光的性能优势,提出了一种波长-能量双色散、激发-发射双聚焦X射线光谱仪(DDF-XRS)设计理念,并成功研制了原理样机。实验数据和分析结果显示,该DDF-XRS型光谱仪兼具聚焦X射线和波长与能量色散光谱仪的优点,结构简单,信噪比好,具有高分辨率和低检出限特性。通过波长-能量双色散技术,X射线首先被晶体衍射发生波长色散,从而获得单色光,同时利用硅漂移探测器的能量色散特性,降低谱线干扰误判风险,提高分析结果准确,该技术克服了WDXRF结构复杂和EDXRF能量分辨率不足的限制,凸显了双色散的必要性和优越性。目前DDF-XRS光谱仪分辨率45 eV,可减少过渡金属K_(β)对K_(α)峰的谱线重叠影响;同时,显著降低了连续谱背景,最优信噪比>1000;测定地质样品中的Cr,检出限可达0.26 mg·kg^(-1)。应用DDF-XRS,一定程度上已可分辨过渡金属K_(α1)和K_(α2)谱线,如结合线性或二维阵列探测器,则有望进一步提高分辨率,实现X射线发射指纹谱的测定,以获得分析元素的化学形态。由于目前的晶体特性尚不能达到完全分辨过渡金属的重叠谱线的性能要求,故探寻具有高分率能力、高衍射强度特性的弯晶,将成为下一步的研究重点。

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 K_(β)to K_(α)peaks;at the same time,it significantly reduces the background of the continuum spectrum,and the optimal signal-to-noise ratio is>1000;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 K_(α1) and K_(α2) 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.