A simple calibration procedure of polycapillary based portable micro‐XRF spectrometers for reliable quantitative analysis of cultural heritage materials

Portable micro‐X‐ray fluorescence (micro‐XRF) spectrometers mostly utilize a polycapillary X‐ray lens along the excitation channel to collect, propagate and focus down to few tens of micrometers the X‐ray tube radiation. However, the polycapillary X‐ray lens increases the complexity of the quantification of micro‐XRF data because its transmission efficiency is strongly dependent on the lens specifications and the propagated X‐ray energy. This feature results to a significant and not easily predicted modification of the energy distribution of the primary X‐ray tube spectrum. In the present work, we propose a simple calibration procedure of the X‐ray lens transmission efficiency based on the fundamental parameters approach in XRF analysis. This analytical methodology is best suited for compact commercial and portable micro‐XRF spectrometers. The developed calibration procedure is validated through the quantitative analysis of a broad range of samples with archeological relevance such as glasses, historical copper alloys, silver and gold alloys offering an overall accuracy of less than 10%–15%. Copyright © 2015 John Wiley & Sons, Ltd.     

Automated printing technology as a new tool for liquid sample preparation for micro x‐ray fluorescence (MXRF)

The focus of this study was to explore automated printing technology (APT) as an alternative means to manual methods for nanoliter dried spot sample preparation of liquid samples for micro x‐ray fluorescence analysis (MXRF). APT was used successfully to dispense 20 and 50 nl volumes of multielemental standard solutions onto AP1 and Kapton film substrates. Automated droplet deposition was rapid and minimized operator skill and human error in the sample preparation process. Dried spots prepared by APT were generally circular in shape and similar in appearance to those prepared by manual dried spot deposition techniques. Furthermore, multiple dried spots could be accurately and reproducibly deposited in the same precise location on the film substrate surface, allowing for increased sample loadings within the MXRF analysis area for higher elemental sensitivity. The characteristics of the substrate did affect the quality of dried spot formation, with irregularly shaped spots forming on the thicker, more hydrophobic Kapton film, especially with higher droplet mass loadings. Adverse effects of irregular spot formation on quantitative analysis could be easily minimized by increasing the MXRF analysis area to encompass the entire dried spot residue. Nanoliter dried spot sample preparation is useful not only for MXRF analysis of liquid samples, but can also be applied to other analytical techniques such as IR, Raman or UV/fluorescence spectroscopy, the applications of which can benefit from rapid sample throughput and matrix reduction. Copyright © 2005 John Wiley & Sons, Ltd.     

Nondestructive elemental depth profiling of Japanese lacquerware ‘Tamamushi‐nuri’ by confocal 3D‐XRF analysis in comparison with micro GE‐XRF

We have applied recently two XRF (micro x‐ray fluorescence) methods [micro‐Grazing Exit XRF (GE‐XRF) and confocal 3D‐XRF] to Japanese lacquerware ‘Tamamushi‐nuri.’ A laboratory grazing‐exit XRF (GE‐XRF) instrument was developed in combination with a micro‐XRF setup. A micro x‐ray beam was produced by a single capillary and a pinhole aperture. Elemental x‐ray images (2D images) obtained at different analyzing depths by micro GE‐XRF have been reported. However, it was difficult to directly obtain depth‐selective x‐ray spectra and 2D images. A 3D XRF instrument using two independent polycapillary x‐ray lenses and two x‐ray sources (Cr and Mo targets) was also applied to the same sample. 2D XRF images of a Japanese lacquerware showed specific distributions of elements at the different depths, indicating that ‘Tamamushi‐nuri’ lacquerware has a layered structure. The merits and disadvantages of both the micro GE‐XRF and confocal micro XRF methods are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A sub‐micrometer resolution hard X‐ray microprobe system of BL8C at Pohang Light Source

A microprobe system has been installed on the nanoprobe/XAFS beamline (BL8C) at PLS‐II, South Korea. Owing to the reproducible switch of the gap of the in‐vacuum undulator (IVU), the intense and brilliant hard X‐ray beam of an IVU can be used in X‐ray fluorescence (XRF) and X‐ray absorption fine‐structure (XAFS) experiments. For high‐spatial‐resolution microprobe experiments a Kirkpatrick–Baez mirror system has been used to focus the millimeter‐sized X‐ray beam to a micrometer‐sized beam. The performance of this system was examined by a combination of micro‐XRF imaging and micro‐XAFS of a beetle wing. These results indicate that the microprobe system of the BL8C can be used to obtain the distributions of trace elements and chemical and structural information of complex materials.     

Improvements of the low‐energy performance of a micro‐focus x‐ray source for XRF analysis with the SEM

X‐ray Fluorescence (XRF) with a scanning electron microscope (SEM) is a valuable completion of the analytical capabilities of SEMs. Small and compact micro‐focus x‐ray sources are mounted to the microscope chamber, and the x‐ray spectra are monitored with conventional EDS systems. Up to now the x‐ray tubes used for the micro‐focus x‐ray sources are equipped with beryllium windows about 100 µm thick. The poly‐capillary x‐ray lenses have their transmission maximum at photon energies around 10 keV. It drops down in both low‐ and high‐energy ranges. Hence, L‐radiation from an Mo or Rh target will be strongly attenuated, and the excitation of fluorescence in the soft x‐ray range becomes very ineffective. A new micro‐focus x‐ray source was developed. It is characterised by a lower self‐absorption in the tube target, thin beryllium windows and an x‐ray optics having a large distance between its foci and the maximum of transmission at about 5 keV. Thus K line fluorescence of light elements becomes effectively excited by the L‐radiation from Mo or Rh tube targets. The detection limit for sodium oxide in glass was found to be below 1 mass%. Copyright © 2009 John Wiley & Sons, Ltd.     

Total reflection x‐ray fluorescence analysis—a review

Total reflection x‐ray fluorescence analysis (TXRF) is a special energy‐dispersive x‐ray analytical technique extending XRF down to the ultra trace element range. Detection limits of picograms or nanograms per gram levels are reached with x‐ray tube excitation. Using synchrotron radiation as excitation source, femtogram levels are detectable, particularly important for Si wafer surface analysis. TXRF is specially suited for applications in which only a very small amount of sample is available, as only a few micrograms are required for the analysis. In this review, an overview of theoretical principles, advantages, instrumentation, quantification and application is given. Chemical analysis as well as surface analysis including depth profiling and thin‐film characterization is described. Special research results on extension to low‐Z elements, excitation with synchrotron radiation and x‐ray absorption spectroscopy (XAS) for chemical speciation at trace levels are reviewed. Copyright © 2007 John Wiley & Sons, Ltd.     

Calculation of attenuation and x‐ray fluorescence intensities for non‐parallel x‐ray beams

With the nowadays widespreaded use of x‐ray optics in x‐ray fluorescence analysis, large convergence or divergence angles can occur. This experimental situation violates a basic assumption of the usual fundamental parameter quantification procedure. In order to take beam divergences in micro x‐ray fluorescence analysis into account, a way of calculating fluorescence intensities numerically by Monte Carlo integration is described. For three examples of typical micro‐XRF set‐ups the fluorescence intensities and their deviation from the parallel beam geometry are calculated. Furthermore, we propose a new approach with ‘equivalent angles’ which correct for the beam divergences in fundamental parameter methods. Copyright © 2003 John Wiley & Sons, Ltd.     

Integrating 3D images using laboratory‐based micro X‐ray computed tomography and confocal X‐ray fluorescence techniques

The application of non‐destructive imaging to characterizing samples has become more important as the costs of samples increase. Imaging a sample via X‐ray techniques is preferable when altering or even touching the sample affects its properties, or when the sample is fielded after characterization. Two laboratory‐based X‐ray techniques used at Los Alamos include micro X‐ray computed tomography (MXCT) and confocal micro X‐ray fluorescence (confocal MXRF). Both methods create a 3D rendering of the sample non‐destructively. MXCT produces a high‐resolution (sub‐µm voxel) rendering of the sample based upon X‐ray absorption; the resulting model is a function of density and does not contain any elemental information. Confocal MXRF produces an elementally specific 3D rendering of the sample, but at a lower (30 × 30 × 65 µm) resolution. By combining data from these two techniques, scientists provided a more comprehensive method of analysis. We will describe a MATLAB routine written to render each of these data sets individually and/or within the same coordinate system. This approach is shown in the analysis of two samples: an integrated circuit surface mounted resistor and a machined piece of polystyrene foam. The samples chosen provide an opportunity to compare and contrast the two X‐ray techniques, identify their weaknesses and show how they are used in a complementary fashion. Copyright © 2010 John Wiley & Sons, Ltd.     

Elemental depth profile of faux bamboo paint in Forbidden City studied by synchrotron radiation confocal µ‐XRF

A three‐dimensional (3D) analysis of micro x‐ray fluorescence (XRF), namely confocal µ‐XRF, has been constructed at 4W1B beamline of the Beijing synchrotron radiation facility (BSRF). A KB mirror is applied to focus the incident beam and a polycapillary half‐lens in front of the Si(Li) detector is used to limit the visual field of the detector. The faux bamboo paint in Emperor Qianlong's Lodge of Retirement in Forbidden City was analyzed nondestructively by this method. A stratified structure in the paint is disclosed and the results show that the painting was probably restored once in the past, following the same painting technique as originally used. Copyright © 2008 John Wiley & Sons, Ltd.     

A new film analysis method using polycapillary X-ray lens

Grazing emission X-ray fluorescence (GE-XRF) is a development of XRF related to total reflection XRF. This paper proposed a GE-MXRF setup involved a polycapillary X-ray lens. Polycapillary lens is an effective optics to obtain μm-size primary X-ray beam. Using this proposed setup, we applied it to the analysis of film samples, and the information of film thickness, composition and density can be acquired, which is very useful in semiconductor industry.     

应用MXRF分析技术测定植物叶片中环境元素

应用一种使用X光透镜的微束X射线荧光(MXRF)分析技术, 对北京不同地区的松针中重金属元素及S元素含量进行了测定和分析, 探讨了它们与大气污染之间的关系; 根据受损松针与正常松针检测结果的比较, 确定了污染元素。 对小叶黄杨叶片中部进行了二维微区自动扫描, 得出了小叶黄杨叶片对各种金属元素的抗污染能力。 研究结果从方法学上验证了使用X光透镜的MXRF分析技术在测量环境样品中的应用, 为环境科研、 污染治理和环境管理提供了科学依据。     

The effects of absorption edge structure of atoms in x‐ray fluorescence analysis

The effects of the absorption edge structure in x‐ray fluorescence (XRF) manifest themselves as a very strong attenuation of the analytical line radiation when it is in the x‐ray absorption near edge structure (XANES) range. In this paper, this effect is exemplified by an ultra‐strong Ba‐caused attenuation of the Ce Lβ₁ line. This case was experimentally studied. Comparison of measured and calculated relative intensities has shown that the actual mass attenuation coefficient of the Ce Lβ₁ line in Ba is 1.6 times greater than known values. This is due to that the Ce Lβ₁ line is within the initial range of L3 Ba absorption edge, i. e. the XANES range. Such an effect of the absorption edge structure of atoms must be considered using the fundamental parameters method in quantitative XRF analysis. This paper also presents some other possible cases of this effect. Copyright © 2009 John Wiley & Sons, Ltd.     

Improvement of peak‐to‐background ratio in PIXE and XRF methods using thin Si‐PIN detectors

This paper describes the peak‐to‐background ratio improvement that can be achieved in PIXE and XRF applications by the use of thin crystal detectors. This improvement becomes apparent in the presence of an intense γ‐ray source, which can be produced either during proton irradiation of a sample (PIXE) or in the deexcitation of the radionuclide in radioisotope‐induced XRF analysis (RIXRF). In order to study theoretically the energy response of a silicon crystal in the x‐ray energy region with respect to its thickness and the energy of the incident γ‐radiation, a Monte Carlo simulation was performed. Experimentally, two detectors having crystal thicknesses of 300 µm and 3 mm were employed in specific analytical applications of PIXE, PIXE‐induced XRF and RIXRF techniques. The peak‐to‐background ratios obtained for various characteristic x‐rays were compared between the two detectors. The performances of the two detectors were also compared in the monochromatic XRF analysis of samples with low average atomic number matrix content. Copyright © 2003 John Wiley & Sons, Ltd.     

利用毛细管X光透镜共聚焦微束X射线荧光技术对单根头发中元素空间分布进行无损扫描分析

头发中的元素与人的饮食和健康状况有关,对头发中元素的分析,不仅可用于刑事物证鉴别,还可为疾病的预防和治疗提供依据,因此,如何检测头发中元素分布等信息倍受人们关注。本文利用基于毛细管X光透镜和实验室普通X射线光源的共聚焦微束X射线荧光技术对单根头进行了无损扫描分析,分析了单根头发中元素的空间分布。在该毛细管X光透镜共聚焦微束X射线荧光技术中,毛细管X光会聚透镜的出口焦斑和毛细管X光平行束透镜的入口焦斑处在共聚焦状态,从而形成共聚焦微元,探测器只能探测到来自该共聚焦微元中的X射线信号,降低了背底信号对X射线荧光谱的影响,从而有利于提高该共聚焦X射线荧光技术的分析精度。该共聚焦技术中采用了具有高功率密度增益的毛细管X光会聚透镜,降低了该共聚焦X射线荧光技术对X射线光源功率的要求,从而保证了该共聚焦技术可以采用实验室普通X射线光源,降低了实验成本。实验表明,毛细管X光透镜共聚焦微束X射线荧光技术在单根头发元素分布检测中具有应用价值。     

Simulation of layer measurement with confocal micro‐XRF

A simple model to simulate the measurement of layered structures with confocal micro X‐ray fluorescence (micro‐XRF) was developed and implemented as a computer program. The model assumes monochromatic excitation, considers at the moment only K lines, and simplifies the volume defined by excitation and detection foci as a circle area. First simulation results and comparison with data acquired using the Atominstitut confocal micro‐XRF spectrometer are very promising. The simulation software enables us to perform parameter studies to have a better understanding of the analysis of layered structures with confocal micro‐XRF. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of ceramic oxide refractories by XRF and XRD

The present study was undertaken to establish a methodology for characterizing ceramic oxide refractory materials, as no detailed information could be found in the literature on this point. The following refractories were analysed: two silica, one alumina, one silica–alumina, two zirconium, three chrome and three magnesia refractories. X‐ray fluorescence (XRF) spectrometry was used for chemical characterization and x‐ray diffraction (XRD) for phase analysis. Phases were determined because of their influence on the end properties of refractory materials. Five analytical programmes for XRF analysis and an XRD analysis method were established. We optimized sample preparation in the form of beads for the XRF measurement by determining the most appropriate sample/flux ratio for each type of refractory. Calibration and validation standards were prepared from mixtures of reference materials, owing to the scarcity of refractory reference materials. The chemical and phase composition of different ceramic oxide refractory bricks was determined and related to the deterioration of these refractories in industrial service, because refractories with a similar chemical composition and different crystalline phases can exhibit different properties. Copyright © 2004 John Wiley & Sons, Ltd.     

Microfluidic sample preparation for elemental analysis in liquid samples using micro X‐ray fluorescence spectrometry

The integration of microfluidic devices with micro X‐ray fluorescence (micro‐XRF) spectrometry offers a new approach for the direct characterization of liquid materials. A sample presentation method based on use of small volumes (<5 µl) of liquid contained in an XRF‐compatible device has been developed. In this feasibility study, a prototype chip was constructed, and its suitability for XRF analysis of liquids was evaluated, along with that of a commercially produced microfluidic device. Each of the chips had an analytical chamber which contained approximately 1 µl of sample when the device was filled using a pipette. The performance of the chips was assessed using micro‐XRF and high resolution monochromatic wavelength dispersive X‐ray fluorescence, a method that provides highly selective and sensitive detection of actinides. The intended application of the device developed in this study is for measurement of Pu in spent nuclear fuel. Aqueous solutions and a synthetic spent fuel matrix were used to evaluate the devices. Sr, which has its Kα line energy close to the Pu Lα line at 14.2 keV, was utilized as a surrogate for Pu because of reduced handling risks. Between and within chip repeatability were studied, along with linearity of response and accuracy. The limit of detection for Sr determination in the chip is estimated at 5 ng/µl (ppm). This work demonstrates the applicability of microfluidic sample preparation to liquid characterization by XRF, and provides a basis for further development of this approach for elemental analysis within a range of sample types. Copyright © 2014 John Wiley & Sons, Ltd.     

A confocal set‐up for micro‐XRF and XAFS experiments using diamond‐anvil cells

A confocal set‐up is presented that improves micro‐XRF and XAFS experiments with high‐pressure diamond‐anvil cells (DACs). In this experiment a probing volume is defined by the focus of the incoming synchrotron radiation beam and that of a polycapillary X‐ray half‐lens with a very long working distance, which is placed in front of the fluorescence detector. This set‐up enhances the quality of the fluorescence and XAFS spectra, and thus the sensitivity for detecting elements at low concentrations. It efficiently suppresses signal from outside the sample chamber, which stems from elastic and inelastic scattering of the incoming beam by the diamond anvils as well as from excitation of fluorescence from the body of the DAC.     

Evaluation of effects of irregular shape on quantitative XRF analysis of metal objects

Quantitative XRF analysis of metal alloys can be obtained by using the general fundamental parameter method based on the comparison of x‐ray line fluorescence intensities with those obtained from reference standard pellets in identical experimental conditions. Corrections for auto absorption and secondary excitation effects are fundamental to obtaining quantitative results. When analyzing a real object with irregular, or at least nonpellet‐shaped, geometry and/or of incorrect positioning, an additional correction factor for x‐ray fluorescence line intensities must be entered. In this paper we review the problem of the contributions to the error specific to an irregular surface or incorrect positioning intrinsic to the fundamental parameter method, in the more enlarged context of considering a real experimental setup in which irradiation and detection angles are not exactly constant, as assumed in the fundamental parameter method. They are accounted for by the corrective irregular shape factors. In principle, these factors must be separately calculated for each value of excitation and characteristic x‐ray energies, and the relative precision in the quantitative determination of elemental concentrations with the fundamental parameter method can be estimated from the relative amplitude of the variation of shape factor values depending on the exciting energy spectrum. One obtains the result that the correction due to irregular shape or incorrect positioning of the object under examination tends to the limit 1, or, more generally, to a constant value independent of the excitation and emission x‐ray energies in the limiting case where the direction of the exciting radiation coincides with that of the detected fluorescence x‐rays. The results of calculations of the relative precision of XRF quantitative analysis are shown for gold‐based alloy objects in some specific cases of surface roughness and positioning of the object. Dispersion around the nominal values for the angles of incoming and outgoing x‐ray directions is assumed as determined by the geometric conditions in two selected instrumental setups. A nominal value of 45° was assumed for both the angles in the first case. In the second case, we considered an irradiation setup where the condition of coincidence for incoming and outgoing x‐ray directions is nearly achieved by employing an annular silicon drift detector (SDD) with a central hole, which allows the passage of the exciting x‐rays. An interesting result obtained in the latter case is that, looking only at the dependence on the irregular shape, an attainable precision on the order of <1‰ can be achieved. In view of the possible applications of quantitative XRF analysis to jewellery, employing SDD detectors capable of very high counting rates should allow a statistical error under the above‐mentioned limit in a reasonably short measuring time. However, concerning the error deriving from intrinsic x‐ray tube instability, an investigation aimed at achieving a stable enough system is still needed. Copyright © 2006 John Wiley & Sons, Ltd.     

Quantitative or semi‐quantitative?–laboratory‐based WD‐XRF versus portable ED‐XRF spectrometer: results obtained from measurements on nickel‐base alloys

‘Semi‐quantitative’ analytical procedures are becoming more and more popular. Using such procedures, the question of the accuracy of results arises. The accuracy of an analytical procedure depends to a great extent on spectral resolution, counting statistics and matrix correction. Two ‘semi‐quantitative’ procedures are compared with a quantitative analytical program. Using a laboratory‐based wavelength‐dispersive x‐ray fluorescence (WD‐XRF) spectrometer and a portable energy‐dispersive x‐ray fluorescence (ED‐XRF) spectrometer, 28 different nickel‐base alloy Certified Reference Materials (CRMs) were analyzed. Line interferences and inaccurate matrix correction are reasons for deviations from the reference value. As the comparison shows, ‘semi‐quantitative’ analyses on the WD‐XRF spectrometer can be accepted as quantitative determinations. The investigations show that the results obtained with the portable ED‐XRF spectrometer do not meet the quality requirements of laboratory analysis, but they are good enough for field investigations. Copyright © 2004 John Wiley & Sons, Ltd.