XRF中激发电位和靶材对散射效应增强荧光强度的影响研究

采用一组熔融片样品研究了由不同的X光管激发电位和不同的X光管靶材(Cr靶和Rh靶)所导致的入射X射线能量及强度分布变化对3种散射效应增强荧光强度的影响规律.研究的散射增强包括相干散射激发的荧光强度、非相干散射激发的荧光强度以及其他方向的一次荧光被散射进探测方向的强度.研究结果表明,对于采用的熔融片,相干散射效应和一次荧光被散射进探测器方向增强效应对荧光强度的贡献随X光管激发电位增大而减小,用Cr靶原级谱激发比用Rh靶原级谱激发贡献大;而非相干散射效应对荧光强度的贡献则随X光管激发电位增大而增大,用Rh靶原级谱激发比用Cr靶原级谱激发贡献大;3种散射效应对荧光强度的总贡献随X光管激发电位增大而增大,在Rh靶原级谱激发条件下比用Cr靶原级谱激发贡献大.     

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。     

X射线荧光分析中X射线管原级能谱分布的测定

确切知道X射线管激发的原级能谱分布是X射线荧光分析中的一个重要前提,所用能谱分布函数的准确度大大影响了最终的测量结果。提出利用间接测量法,选用合适的参量模型来描述X射线的原级能谱分布。依靠实验测得的厚靶纯元素样品的荧光强度,利用已知的理论公式,建立非线性方程,优化得到参量模型中的参量值。通过比较实验测得的元素的荧光强度值和利用得到的能谱分布函数计算的理论值,证明此种方法是可行的。     

X射线荧光光谱检测多层薄膜样品的增强效应研究

研究了X射线荧光光谱检测多层薄膜样品的增强效应.根据多层膜中的X荧光强度理论计算公式编写了计算机程序,并计算了Zn/Fe和Fe/Zn双层膜样品中不同薄膜厚度时Fe Kα的一次荧光强度、二次荧光强度、二次荧光与一次荧光强度比以及二次荧光在总荧光强度中比例.研究发现,在多层膜样品的X射线荧光分析中,激发条件不变的情况下,元素谱线的一次荧光相对强度、二次荧光相对强度和二次荧光在总荧光强度中所占比例都随薄膜厚度及位置的变化而变化.当Fe和Zn层厚度相同时,随厚度的变化,对于Fe/Zn样品,Fe Kα二次荧光强度占总荧光强度最高为9%,而对于Zn/Fe样品这一比例最高可达35%.     

能量色散X荧光分析中元素间效应的蒙特卡罗模拟

针对能量色散X荧光分析(EDXRF)技术中元素间效应实验研究的难点问题,采用蒙特卡罗方法对基于Si（PIN）探测器的EDXRF系统建立模拟模型,并对模拟微束软X射线注量谱建立了高斯展宽算法。对Fe-Ni样品进行模拟计算,表明经该算法展宽后的注量谱与实测K系特征X射线谱吻合度较高,并得到了各元素特征X射线归一计数与元素含量关系曲线,结果表明该方法可自行校正EDXRF中元素间效应,获得准确的元素K系特征X射线谱理论强度。     

同步辐射X射线荧光分析

 近二、三十年来,X射线荧光分析(简称XRF)已成为物质中元素含量分析的基本手段,已广泛应用于物理、化学、生物、医学、法学、地学、材料科学等学科及工农业生产中.XRF是用X射线激发样品,并检测从样品中发射出的元素之特征X射线强度,分析样品中元素的含量.所谓特征X射线,是指每种元素的原子受激后会发射特定能量的X射线,它们是不连续的,是各自分立的.当原子内壳层中的电子受外来粒子作用而电离后,就会在内壳层留下一个空穴,于是较外层的电子就会跃迁到这个空穴,这就是所谓的退激发过程.     

偏振X射线荧光系统测量痕量Cd元素的Geant4模拟研究

通过传统能量色散X射线荧光分析(EDXRF)对Cd元素进行痕量分析时,X光管发出的原级轫致辐射连续谱对Cd元素的分析具有严重的影响。为了减弱原级X射线对测量结果的影响,通过Geant4程序包模拟不同几何尺寸下偏振激发X射线荧光分析(P-EDXRF)中荧光靶的结构,研究其在减弱测量过程中原级X射线轫致辐射连续谱的影响。为了提高模拟效率,本文分三步进行模拟。第一步模拟不同管电压下电子打靶过程,得到不同管压下的X光管原级能谱。第二步针对Cd元素的痕量分析设置不同种类、不同几何条件的Te及BaSO₄作为荧光靶材料进行模拟。结果表明在使用K_α1能量(27.468 keV)与Cd元素吸收限26.711 keV最为接近的Te作为荧光靶材料时,随着Te靶厚度增加Te元素的特征峰强度在100 μm前快速增长,在150 μm后趋于稳定。而其信噪比(SNR)在80 μm到达最大值21.434。继续增加厚度由于荧光靶材料的自吸收作用SNR开始有些许下降,达到饱和吸收厚度后稳定。在不同应用场景时荧光靶选材应有不同,对于测量时间没有限制的条件下,应选择荧光强度更大的荧光靶厚度。而对于测量时间相对较短的条件下,则应该选择SNR更大的荧光靶厚度。第三步模拟通过荧光靶后的出射能谱激发含0.01%Cd的样品,经过Te靶后的出射能谱激发样品,得到Cd元素K_α1峰背比为8.28。相较于直接通过原级谱激发样品,Cd元素K_α1峰背比为2.29,其峰背比明显提高但Te元素的散射峰对Cd元素K_α1峰仍然有所影响。选用特征X射线能量与Cd元素K_α1相距更远的BaSO₄作为荧光靶材料,可减弱由于样品中的基体轻元素的散射作用而引起目标元素的峰背比降低情况,可将Cd元素K_α1峰背比提高至14.179。通过增大X光管管电压可进一步提高激发效果,在管电压为70 kV时对于Cd元素有最佳激发效果,峰背比为21.431。     

用蒙特-卡罗方法模拟质子X荧光分析中的荧光增强因子

本文用蒙特-卡罗方法模拟质子激发X荧光分析中的一次和二次荧光强度,从而得到荧光增强因子。文中利用模拟计算程序,在改变入射质子能量、入射角、x射线出射角及分析样品的成分和含量的条件下,分别计算了荧光增强因子。此外,还计算了质子激发标准合金钢样品的荧光增强因子,得到的     

土壤重金属铅元素的X射线荧光光谱测量分析

在实验室条件下,利用NITON XLt793型便携式X射线荧光光谱重金属分析仪测量并分析土壤中铅元素的X射线荧光光谱特性。分别以铅的Lα(10.55keV)和Lβ(12.61keV)特征谱线作为分析线,分析了不同基体元素对分析线的影响;测定在不同铅浓度下的特征谱线强度变化。结果表明铅的质量分数在10×10-6～1 800×10-6范围内,元素的光谱强度与浓度之间呈现较好的线性关系;建立了铅元素的定标曲线,并计算得到铅的检出限为7.89×10-6。     

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7keV)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7keV),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0.96~2.24mm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。     

Effect of hydrogen adsorption on the x-ray absorption spectra of small Pt clusters

Hydrogen adsorption on Pt(6)H(n) clusters leads to striking changes in the Pt L(2,3) x-ray absorption spectra. These effects are interpreted using a self-consistent real space Green's function approach. Calculations show that they are due largely to changes in the atomic background contribution to x-ray absorption (i.e., atomic x-ray absorption fine structure) and to reduced Pt-Pt scattering at the edge, while Pt-H multiple scattering is relatively weak. The origin of both effects is traced to the change in the local Pt potential due to Pt-H bonding.     

Quantitative evaluation of equatorial small-angle X-ray scattering for cylindrical fibers

Elongated microvoids, internal fibrillar structure, and edge scattering from both surface refraction cause an equatorial streak in small angle X-ray scattering. A model for analyzing the edge scattering of fibers is proposed. Simulation results indicate that the intensity of edge scattering from surface refraction of a cylindrical fiber is strong and makes an important contribution to the equatorial streak. Two factors influence edge scattering intensity. One is the sample-to-detector distance (D); edge scattering intensity increases with increasing D. The equatorial streak becomes weak when D is shortened. The other factor is the refraction index. Edge scattering intensity increases as the real component of the refraction index decreases. In experiment, weak or even no equatorial streaks were found for samples measured in a roughly index-matching fluid. Edge scattering can be eliminated or weakened, and it can be calculated by comparing the intensities of a cylindrical fiber when it is measured in air and in index-matching fluid. The simulation data are basically in agreement with the experimental data.     

K‐edge XANES analysis of sulfur compounds: an investigation of the relative intensities using internal calibration

Sulfur K‐edge XANES (X‐ray absorption near‐edge structure) spectroscopy is an excellent tool for determining the speciation of sulfur compounds in complex matrices. This paper presents a method to quantitatively determine the kinds of sulfur species in natural samples using internally calibrated reference spectra of model compounds. Owing to significant self‐absorption of formed fluorescence radiation in the sample itself the fluorescence signal displays a non‐linear correlation with the sulfur content over a wide concentration range. Self‐absorption is also a problem at low total absorption of the sample when the sulfur compounds are present as particles. The post‐edge intensity patterns of the sulfur K‐edge XANES spectra vary with the type of sulfur compound, with reducing sulfur compounds often having a higher post‐edge intensity than the oxidized forms. In dilute solutions (less than 0.3–0.5%) it is possible to use sulfur K‐edge XANES reference data for quantitative analysis of the contribution from different species. The results show that it is essential to use an internal calibration system when performing quantitative XANES analysis. Preparation of unknown samples must take both the total absorption and possible presence of self‐absorbing particles into consideration.     

Theoretical interpretation of spin-polarized X-ray absorption spectra of Mn in MnP

On the basis of the multiple scattering approach in combination with the spin-polarized self-consistent potential calculation, an interpretation is proposed for the spin-polarized x-ray absorption spectra near the Mn K edge in MnP. The effect of the core vacancy potential on the spectra is analyzed and found to be insignificant. The method used for the calculations allowed the separation of the effect of the dipole transition matrix element on the spectra and the effect of the density of unoccupied electron states. It is shown that the transition matrix element causes an intensity redistribution only near the absorption jump, while the difference in the densities of states is most pronounced in the energy region 35–55 eV away from the main edge and leads to a shift in energy for the spectra corresponding to the two spin directions. The effect of the spin-dependent broadening caused by the dependence of the mean free path (as a function of energy) on the photoelectron spin is studied. It is shown that this factor considerably affects only the intensities of the peaks in the energy region lying within less than 12 eV from the main edge.     

Algorithm of fundamental parameters for the SEICXRF method

An algorithm based on fundamental parameters and applied to the SEICXRF method, developed by one of the authors, is presented. The methodology used in the calculation is similar to the Rousseau fundamental parameters method, but the main difference is the considerations about the x‐ray secondary fluorescence. In the new experimental method, the fluorescence yield by photons corresponding to the absorption edges with energies greater than the absorption edge energy of analyte does not occur. This secondary fluorescence appears in the calculation of the total fluorescence as a consequence of the integral count of the fluorescent emission from the sample. It is created by the primary fluorescence yield of the atoms whose absorption edge energies are less than the primary fluorescence energy of the analyte. The algorithm also considers the effect of the decrease of the sample fluorescent background just at the jump, originated by the change of the absorption coefficient at the absorption edge energy of the element of interest. Considering these two effects, including the primary fluorescence in the calculation, allows one to obtain the net fluorescence originated by the analyte at its own absorption edge. Copyright © 2003 John Wiley & Sons, Ltd.     

Atomic and solid-state effects in the angle resolved photoemission cross section from an adsorbate: 4d levels of c(2 × 2)Te on Ni

The photon energy dependence of the normal emission from the Te - 4d levels of an ordered Te c(2 × 2) overlayer on Ni(100) shows two distinct types of structure. The main feature is due to an atomic effect, a delayed onset, a peak followed by a Copper minimum. Superimposed on this atomic profile are intensity modulations of 30 to 40% due to coherent scattering from the substrate. The atomic contribution is in qualitative agreement with theoretical calculations, while the modulations due to solid-state effects are not reproduced by a LEED final state type calculation.     

人体血清中胆红素荧光光谱初步分析

利用分子荧光和紫外-可见吸收光谱仪分别测定了在模拟生理条件下的胆红素、胆红素和牛血清白蛋白混合溶液的荧光光谱和吸收光谱,同时也测定了一些体检者血清样品的荧光发射光谱。实验结果表明:不同情况下的胆红素溶液具有不同的荧光光谱和吸收光谱;血清白蛋白对胆红素荧光具有增敏效应。此外,初步认为所测得的人体血清样品位于约524 nm处的荧光不是主要来自于人体血清中白蛋白结合形式的胆红素组分贡献。