毛细管聚焦的X射线荧光光谱拟合软件的开发及应用

基于Python语言设计了一款毛细管聚焦的X射线荧光光谱拟合软件QMXRS（quantitative analysis of micro-energy dispersive X-ray fluorescence spectra）并实现其在毛细管聚焦的X射线荧光光谱拟合方面的应用。QMXRS具有小波降噪、本底扣除、能量刻度、元素特征峰的识别、分峰和拟合、能谱的批处理和元素分布成像等功能。毛细管聚焦的X射线荧光分析技术采用毛细管X光透镜对X射线源激发出的X射线束进行聚焦导致X射线荧光光谱分布发生改变。这一变化影响了毛细管聚焦的X射线荧光光谱本底分布。因此QMXRS利用本底预估模型对毛细管聚焦的X荧光光谱本底进行本底分布的修正;同时在全谱拟合过程中,利用半高宽与能量的关系对高斯峰半高宽进行约束,减少高斯峰模型中变量,在保证全谱拟合收敛的同时提高了拟合速度。为验证上述方法的可行性,分别利用QMXRS,PyMca(python multichannel analyzer)和QXAS(quantitative X-ray analysis system)三款软件分析NIST 610标准样品的毛细管聚焦的微束X射线荧光光谱,并对比三款软件的元素特征峰拟合结果。结果表明,相较于QXAS和PyMca采用的非最小二乘法拟合,QMXRS采用约束化的非线性最小二乘法进行拟合能有效的减少能谱拟合过程中带来的误差,提高分析数据的准确度。     

MC模拟分析透射式微型X射线管目标靶厚度对输出谱的影响

透射式微型X射线管是能量色散X射线荧光分析中的主要激发源,在能量色散X射线荧光分析中希望得到谱分布较为单一的X射线管输出谱。采用MC方法,研究了透射式微型X射线管在不同目标靶厚度的情况下输出谱的特征,通过低谱段(<5 keV)和高能谱段(5~50 keV)的分析比较,高能谱段计数随厚度加大先增加而后减小,低能谱段计数则随厚度增加减小,增加目标靶厚度可以有效抑制低能谱段。在入射电子能量为50 keV和目标靶为4 Ag的条件下,X射线管输出能谱具有较高的高能谱段注量,同时有效压制低能谱段注量,适合能量色散X射线荧光分析中使用。     

微型X射线管出射谱特征研究及Be窗厚度确定

微型X射线管已广泛应用于现场元素分析、放射性医疗等领域,对于微型X射线管铍窗,普遍认为除保证管内真空外,应越薄越好。采用蒙特卡洛方法,模拟了从50～500 μm范围内共13个Be窗厚度的微型X射线管出射X射线谱。按照在应用中的作用,将出射X射线划分为不同能量段进行分析。通过分析谱线特征,发现Be窗厚度应依据其应用要求合理选择。因此,提出了K系特征X射线与轫致辐射强度的比值和低能射线与激发射线计数比值等参量作为评价Be窗厚度最优化的判断依据。除上述评判指标外,铍窗的厚度最优化选择还应考虑Be窗对不同能量X射线的屏蔽效果。依据模拟结果分析,原位(现场)X射线能量色散荧光分析应用中,Be窗厚度约250 μm的微型X射线管最为合适。与50 μm铍窗厚度出射射线相比,71.66%低能原级X射线被屏蔽,5~50 keV能量原级X射线仅有21.31%被屏蔽,低能射线强度占总X射线比值小于10%,且K系X射线占激发射线的比例仍保持较高的水平。因此,采用250 μm铍窗厚度的微型X射线管作为能量色散激发源,能保证探测器探测的有效信号比值较高,低能X射线对探测器的能量分辨率的影响最小,而且能量色散分析谱线的散射本底相对强度处于较低的水平,从而保证元素分析结果精准度。对于放射性治疗的应用中,则铍窗厚度越薄越好,此时,低能X射线具有较高的通量,能保证辐射剂量在治疗组织中剂量的集中。     

薄膜法X射线荧光测量中样品检测位置及防护铅板内衬材料的选择研究

(1)以型号316不锈钢金属板为研究对象,对薄膜法X射线荧光光谱测量中,样品检测位置的选择进行研究,确定了最佳的样品检测位置为样品距离X射线管和探测器水平基线1 cm处,并且与X射线管和探测器水平基线成16°角度。(2)以工业环境空气重金属污染物Pb,Cd,Cr为主要分析对象,在有铅板防护情况下进行薄膜法X射线荧光光谱测量研究,发现X射线会穿透样品薄膜而继续激发防护铅板,使得滤膜背景光谱中有较强的铅谱线干扰,会对实际样品中铅元素的测量产生影响。在薄样和防护铅板之间加上一层隔离材料,可有效避免防护铅板中铅谱线对样品测量产生的干扰。(3)以型号316不锈钢、黄铜、铝材、紫铜和聚四氟乙烯几种硬质隔离材料作为铅板内衬材料进行选择研究,结果表明：紫铜的X射线荧光光谱中所含元素的谱线最少,谱图中没有出现重金属Cr,Cd,Pb的谱峰,并且能量较高部分靶材散射光谱强度较弱,对实际样品中重金属元素Cr,Cd和Pb的测量不会产生干扰,作为铅板的内衬金属材料可以避免防护铅板中铅元素谱线的干扰,是最佳的薄膜法X射线荧光光谱分析中铅板的内衬金属材料。该研究为组装及搭建便携式大气及水体重金属X射线荧光光谱分析仪提供了重要的理论依据。     

薄膜法X射线荧光测量中样品检测位置及防护铅板内衬材料的选择研究

(1)以型号316不锈钢金属板为研究对象, 对薄膜法X射线荧光光谱测量中, 样品检测位置的选择进行研究, 确定了最佳的样品检测位置为样品距离X射线管和探测器水平基线1 cm处, 并且与X射线管和探测器水平基线成16°角度。(2)以工业环境空气重金属污染物Pb, Cd, Cr为主要分析对象, 在有铅板防护情况下进行薄膜法X射线荧光光谱测量研究, 发现X射线会穿透样品薄膜而继续激发防护铅板, 使得滤膜背景光谱中有较强的铅谱线干扰, 会对实际样品中铅元素的测量产生影响。在薄样和防护铅板之间加上一层隔离材料, 可有效避免防护铅板中铅谱线对样品测量产生的干扰。(3)以型号316不锈钢、黄铜、铝材、紫铜和聚四氟乙烯几种硬质隔离材料作为铅板内衬材料进行选择研究, 结果表明: 紫铜的X射线荧光光谱中所含元素的谱线最少, 谱图中没有出现重金属Cr, Cd, Pb的谱峰, 并且能量较高部分靶材散射光谱强度较弱, 对实际样品中重金属元素Cr, Cd和Pb的测量不会产生干扰, 作为铅板的内衬金属材料可以避免防护铅板中铅元素谱线的干扰, 是最佳的薄膜法X射线荧光光谱分析中铅板的内衬金属材料。该研究为组装及搭建便携式大气及水体重金属X射线荧光光谱分析仪提供了重要的理论依据。     

X射线荧光测井谱漂校正技术研究

X射线荧光测井技术是一种可以在井下原位进行元素定量(半定量)分析的测井技术,对矿产勘查具有重要意义。受井下温度影响,X射线荧光测井仪容易发生谱漂。X射线测井仪采用硬件进行稳谱,采用软件实现微小谱漂校正。X射线荧光测井的谱数据量大,难以采用人工校正的方法实现。文章在总结了X射线荧光测量专业人员进行谱漂校正经验的基础上,结合专家系统研究了X射线荧光测井谱漂的校正方法。在谱漂校正过程中,采用对散射本底变化不灵敏的对称零面积法进行自动寻峰,并用标准方差进行指示峰判别。利用先验知识(上一次能量刻度)和高斯概率密度函数对当前指示峰进行定性分析,确定指示峰能量。将指示峰峰位和定性分析获得的能量值采用最小二乘法进行拟合,获得能量刻度系数,并对偏离较大的数据进行筛选,达到能量自动刻度目的,实现X射线荧光测井仪器谱谱漂校正。文章采用所述的谱漂校正方法对某次X射线测井仪温度实验的322条谱线进行校正,结果表明该方法能够有效地自动校正X射线荧光测井仪谱漂。     

原位能量色散X射线荧光分析中岩样基体效应及其修正研究

原位能量色散X射线荧光现场分析岩样矿物成分时,岩样基体效应会对测量结果产生影响。本文以Cu元素作为待测元素,研究了17种不同岩样基体对原位能量色散X射线荧光分析Cu元素特征X射线强度的影响及其修正方法。采用蒙特卡罗方法模拟获得了Cu元素含量相同的17种不同岩样测量谱线,综合各类岩石元素构成的相似性,并依据模拟谱线Cu元素Kα射线强度与谱线参数之间的相关性,反映了原位能量色散X射线荧光分析岩样Cu元素的基体效应并不完全受岩体元素构成或岩石分类的控制,需要依据岩石样分析谱线参数的相关性进行归类讨论。针对基体影响Cu元素特征射线强度相似的15种岩样进一步研究,并对Cu元素特征X射线与谱线主要参数的主成分进行分析,发现散射本底、X光管靶材料特征X射线及其非相干散射峰强度能够很好的描述Cu元素特征X射线强度受岩样基体影响的变化,据此可以对基体效应影响相似的岩体进行Cu元素测量结果修正。采用本文方法同样也能为不同岩性岩体其他待测元素基体效应的修正提供参考。     

衍射分析用的X射线管谱线纯度的定量测定

本文提出了衍射分析用的X射线管谱线纯度的定量测定方法。在国产衍射仪上用石英单晶作分光晶体进行展谱测定。实验测得的各种波长X射线的强度应还原为X射线管窗口处的出射强度。对影响强度的各种因素作了详细的理论分析,给出了对应于不同靶、不同杂质元素的强度还原换算因子表。X射线管阳极靶元素主特征谱线强度用铜或铝吸收箔进行衰减,以避免计数损失造成的误差。用这一方法,对许多X射线管进行了测定。 关键词：     

原级X射线谱强度分布的定量测定

本文提出了衍射或荧光分析用的X射线管原级X射线谱强度分布的定量测定方法。在带有正比、闪烁计数管的衍射仪上用LiF分光晶体进行展谱测定。实验测定强度经校正计算还原为X射线管窗口处的强度。对荧光X射线管还应测定几个射线束方向的原级谱加以平均求得有效原级谱。分析了原级X射线谱数据的误差及其对基本参数法等实际应用的影响。 关键词：     

X射线激发发射谱仪的研制

通过X射线管与光谱仪的组合,在对X射线管和光谱仪的选取、自动控制技术、数据采集和处理等多个环节进行系统论证的基础上,自行设计和研制了一台X射线激发发射谱仪。通过采用标准光源,对谱仪的波长和效率定标进行了重点研究,运用这一谱仪分别测量了BaF₂和CsⅠ(Tl)等闪烁晶体的X射线激发发射谱。实验结果表明:该谱仪具有光谱分辨高、性能稳定、操作简便、屏蔽良好等特点,可为闪烁材料的探索和开发提供一种十分有效的研究手段。     

Background estimation based on Fourier Transform in the energy‐dispersive X‐ray fluorescence analysis

This paper discusses a new method of background estimation in the energy‐dispersive X‐ray fluorescence (EDXRF) analysis, which is based on Fourier Transform (in this paper, we call it Fourier Transform background estimation method). Compared with the Sensitive Nonlinear Iterative Peak method, the new method has the feature of FWHM independence. It has been proved that a background can be estimated automatically and accurately by the new method in the synthesized spectrum and the spectra from measurement. Fourier Transform background estimation method can estimate the background accurately in the EDXRF spectrum using an X‐ray tube source. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of kernel emission spectrum of a mini X‐ray tube for EDXRF applications

Knowing the spectrum near the output of the relatively new mini X‐ray tube (MXRT) commercial models is fundamentally important in energy‐dispersive X‐ray fluorescence scan images, especially in the in vivo applications. This information is relevant for determining the absorbed dose during a measurement and for absolute quantification by a fundamental parameter method. However, it is not possible to measure it directly using a silicon drift detector (SDD) given the high saturation in the counts. In this work, an experimental methodology is developed for determining the kernel spectrum emitted by the MXRT, enabling the quantification of its energy flux density over short distances. Different distances were used: source–detector, solid emission angle (collimation), attenuation characteristics of the medium (air), and in a vacuum, within an energy range of 1–40 keV, to determine the X‐ray tube spectrum. The spectrum is measured by an SDD, taking its efficiency and dead time into account. In order to verify the method, a spectrum that is rebuilt starting with the kernel is compared, under the same conditions, with a reference spectrum that is directly measured in air and with a theoretical spectrum obtained by the Ebel model. The results are consistent and validate the methodology employed in this work. Additionally, low‐energy peaks were detected, corresponding to the tube material's L lines, which are not present in the original spectrum reported by the manufacturer. Copyright © 2015 John Wiley & Sons, Ltd.     

A background subtraction approach based on complex wavelet transforms in EDXRF

Subtracting the background accurately is one of the most important issues in energy‐dispersive X‐ray fluorescence (EDXRF) spectra processing. This paper presents a novel approach to perform background subtraction based on dual‐tree complex wavelet transform. Compared with real wavelet transform, the proposed method has some attractive properties, including a smooth, nonoscillating, and nearly shift‐invariant magnitude with a simple near‐linear phase encoding of signal shifts. Therefore, it outperforms real wavelet transform to decompose background into low‐frequency components. The effectiveness of the proposed approach is demonstrated via two simulated spectra with different kinds of backgrounds and one measured spectrum from an energy‐dispersive X‐ray spectrometer. Both simulated and experimental results prove that the proposed approach can subtract background in EDXRF spectra effectively. Copyright © 2014 John Wiley & Sons, Ltd.     

A new microfocus x‐ray source,iMOXS, for highly sensitive XRF analysis in scanning electron microscopes

Scanning electron microscopes are usually equipped with energy‐dispersive X‐ray detectors for electron probe microanalysis. This widespread analytical method allows investigators to determine the elemental composition of specimens with a spatial resolution of about 1 µm. However, owing to the electron–specimen interaction, the emitted spectra reveal, in addition to characteristic lines, also a high level of continuous bremsstrahlung background. As a result, elements with low concentrations cannot be identified. The minimum detection limit can be diminished by two orders of magnitude if the characteristic lines are excited as fluorescence by an additional x‐ray source. In this case, the emergence of bremsstrahlung is considerably reduced. Combining a high‐brilliance microfocus x‐ray tube with efficient polycapillary optics enables one to realize an experimental arrangement for performing local fluorescence analysis at the same point where the electron beam hits the sample. The polycapillary optics under consideration focuses the emitted x‐radiation onto focal spots between 30 and 100 µm in diameter. Count rates of several thousands cps have been achieved. Elemental maps have been obtained by means of the motorized specimen stage of the microscope. Copyright © 2005 John Wiley & Sons, Ltd.     

A new way of measuring the contribution of scattered photons to x‐ray fluorescence yields in secondary excitation mode

The characteristic K x‐rays from a secondary exciter in conjunction with an x‐ray tube or a radioisotope as primary source are frequently used for target excitation in x‐ray fluorescence measurements. In this experimental arrangement, the exciting photon spectrum consists of two parts: (i) characteristic K x‐rays of the secondary exciter and (ii) photons from the primary source, which are scattered from the secondary exciter. A new method is proposed for correcting the observed target x‐ray yield due to unwanted excitation by the scattered photons. This method involves measurement of x‐ray yield after replacing the secondary exciter by an equivalent exciter consisting of a low‐Z element foil with a high‐Z element backing. Copyright © 2004 John Wiley & Sons, Ltd.     

样品厚度对薄膜法X射线荧光光谱测量的影响研究

分别以富集有Cr,Pb和Cd三种元素的尼龙薄膜样品及玻璃纤维滤膜为研究对象,采用滤膜叠加的方式,通过XRF光谱仪测量不同样品厚度下薄膜样品的XRF光谱,根据测得的尼龙薄膜样品中Cr,Pb,Cd元素及玻璃纤维滤膜中Ca,As和Sr元素特征XRF性质的变化,研究样品厚度对薄膜法XRF光谱测量的影响。结果表明：薄膜样品厚度对不同能量区间上元素特征谱线荧光性质的影响并不相同。元素特征谱线能量越大,元素特征X射线荧光穿透滤膜到达探测器的过程中损失越少;但由薄膜样品厚度增加引起的基体效应却越强,相应特征谱线位置处的背景荧光强度就越大,因此样品厚度增加所引起的基体效应对薄膜法XRF光谱测量的灵敏度影响就越大。对于特征谱线能量较低(能量小于7 keV)的元素,以增加薄膜样品厚度的方式来增加待测组分的质量厚度浓度,并不能有效地提高薄膜法XRF光谱测量的灵敏度;对于特征谱线能量较高的元素(能量＞7 keV),可以通过适当增加样品厚度以增加被测组分的质量厚度浓度的方式来提高XRF光谱测量的灵敏度,薄膜样品厚度在0.96～2.24 mm内,更有利于XRF光谱的测量与分析。该研究为大气及水体重金属薄膜法XRF光谱分析中薄样制备及富集技术提供了重要的理论依据。     

X‐ray fluorescence determination of sulfur chemical state in sulfide ores

This paper describes the X‐ray fluorescence technique for estimation of the ratio between sulfide and total sulfur in sulfide ores using the influence of sulfur chemical state on positions and intensities of lines (SKα_1,2, SKβ_1,3) and satellites (SKβ′, SKα_3,4) of the sulfur X‐ray emission spectra measured by the wavelength‐dispersive X‐ray fluorescence spectrometer. The samples to be analyzed were prepared as pressed powder pellets on boric acid substrate. The SKα_1,2 line chemical shift is the most appropriate parameter for sulfur chemical state estimation because spectral lines in this field are intensive and are almost not affected by spectral overlap of lead spectrum lines. The ratios of line intensities SKβ′/SKβ_1,3, SKα_3,4/SKα_1,2 and SKβ_1,3/SKα_1,2 were also used as analytical parameters. Forty‐one samples of sulfide ores collected in the Russian Far East and Southern Ural deposits have been analyzed. The results of estimation of sulfur chemical state by gravimetric and proposed X‐ray fluorescence techniques agree fairly well. Copyright © 2016 John Wiley & Sons, Ltd.     

Measurement of L subshell fluorescence yield ratios of some high Z elements by selective excitation method

The L₁, L₂ and L₃ subshells of Hf, Ta and Re atoms have been excited selectively by using microprobe XRF beam line, Indus‐2, RRCAT, India. The consequent characteristic L X‐ray photons, emitted from the targets due to creations of vacancies in L subshells, are measured using silicon drift detector (X‐123) spectrometer. As the energy of synchrotron radiation increases, the contribution of characteristic L X‐ray intensity increases. The advantage of the increase in the intensity of the characteristic L X‐ray photons with an increase in the energy of synchrotron radiation has been used to determine the L subshell fluorescence yield ratios of Hf, Ta and Re atoms by adopting the selective excitation method. The measured ratios of L subshell fluorescence yield have been compared with theoretical and other experimental values.     

A comparative study on determination of uranium and thorium in their mixed oxides by EDXRF using tube and radioisotope X‐ray sources

Studies on the matrix effects of uranium and thorium on the determinations of each other in their mixed oxides using energy dispersive X‐ray fluorescence (EDXRF) spectrometry with tube and radioisotope excitations of U Lα and Th Lα are reported. An internal standard method for the determination of uranium and thorium in these mixed oxides is found suitable. Comparison of the analytical results of EDXRF determinations of uranium and thorium using tube and radioisotope excitation sources has been made. The analytical methodology involves preparation of mixed oxide calibration/sample mixtures of uranium and thorium oxides, mixing of internal standard yttrium in these mixtures, pelletizing the mixtures after thorough mixing and grinding using boric acid binder and measuring EDXRF spectra of the specimens thus prepared using Rh X‐ray tube as well as ¹⁰⁹Cd radioisotope source. The samples were analyzed for uranium and thorium on the basis of the calibration plots obtained by plotting the intensity ratios of the analyte and internal standard characteristic X‐ray lines and their corresponding amount ratios. An average precision of 1.2% (1 s RSD) was observed for the determination of U and Th and the results deviated from the corresponding expected values by 3% on average. Due to the refractory nature of thorium oxide, comparatively more grinding time was required for thorium determinations. Copyright © 2011 John Wiley & Sons, Ltd.     

不同激发方式对能量色散X射线荧光法测铀的影响

针对能量色散X射线荧光法测铀过程中存在自激发效应对测量结果产生干扰的问题及以往测铀仅使用放射性同位素源作为激发源的测量限制,利用微型X射线对铀矿样品进行自激发效应测量,并分别将109Cd,241Am,微型X光管三种不同激发源测量铀矿样品的结果进行比较分析。结果表明,自激发效应产生的特征X射线峰面积计数仅为有源条件的0.01%以下,属统计涨落范畴,对测量结果的干扰可忽略不计;109Cd源由于其特征射线能量22.11和24.95 keV均在L_α吸收限能量21.75 keV附近,激发光电截面最高,相应的荧光产额也高,故109Cd源相比于241Am源对铀元素的激发效率更高;241Am源测量误差明显大于109Cd源的测量误差,原因是铀的L系能量特征峰与241Am源特征射线26.35 keV的散射峰能量区叠加,造成实测谱线本底偏高;X光管作激发源的铀矿样品中铀含量与化学分析结果之间的误差在10%以内,仅为同位素源激发X射线荧光分析误差的一半,且X光管激发谱峰面积计数值明显大于源激发条件下的峰面积计数,说明X光管作激发源的测铀质量优于源激发模式。