Comparison of the detection limits in the analysis of some medium atomic number elements measured with a portable XRF and an external proton beam PIXE spectrometer system

A portable X‐ray fluorescence (XRF) spectrometer system was constructed using an Amptek Mini‐X X‐ray tube and an X‐123 compact spectrometer. The spectrometer is optimised for the best limits of detection. Its analytic properties are tested and compared with an analogous laboratory‐based instrument, an external beam proton‐induced X‐ray emission spectrometry (PIXE) setup. Depending on elements in question the thick target detection limits of this portable XRF device are comparable or even lower than the PIXE setup. Copyright © 2011 John Wiley & Sons, Ltd.     

Monte Carlo simulation code for confocal 3D micro‐beam X‐ray fluorescence analysis of stratified materials

Stratified materials are of great importance for many branches of modern industry, e.g. electronics or optics and for biomedical applications. Examination of chemical composition of individual layers and determination of their thickness helps to get information on their properties and function. A confocal 3D micro X‐ray fluorescence (3D µXRF) spectroscopy is an analytical method giving the possibility to investigate 3D distribution of chemical elements in a sample with spatial resolution in the micrometer regime in a non‐destructive way. Thin foils of Ti, Cu and Au, a bulk sample of Cu and a three‐layered sandwich sample, made of two thin Fe/Ni alloy foils, separated by polypropylene, were used as test samples. A Monte Carlo (MC) simulation code for the determination of elemental concentrations and thickness of individual layers in stratified materials with the use of confocal 3D µXRF spectroscopy was developed. The X‐ray intensity profiles versus the depth below surface, obtained from 3D µXRF experiments, MC simulation and an analytical approach were compared. Correlation coefficients between experimental versus simulated, and experimental versus analytical model X‐ray profiles were calculated. The correlation coefficients were comparable for both methods and exceeded 99%. The experimental X‐ray intensity profiles were deconvoluted with iterative MC simulation and by using analytical expression. The MC method produced slightly more accurate elemental concentrations and thickness of successive layers as compared to the results of the analytical approach. This MC code is a robust tool for simulation of scanning confocal 3D µXRF experiments on stratified materials and for quantitative interpretation of experimental results. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

EDXRF and multivariate statistical analysis of fragments from Marajoara ceramics

In this work, 102 fragments of Marajoara ceramics, belonging to the National Museum collection (Rio de Janeiro, Brazil), were analyzed using energy dispersive X‐ray fluorescence (EDXRF) and principal component analysis (PCA) in order to identify possible groups of samples that present similar behaviors or different characteristics. This information will give an important aid to a more accurate classification of these artifacts. The EDXRF measurements were carried out with a portable system developed in the Nuclear Instrumentation Laboratory consisting of an Oxford TF3005 X‐ray tube, with W anode, and an Si‐PIN XR‐100CR detector from Amptek, working at 25 kV and 100 µA, acquisition time of 600 s and a beam collimation of 2 mm. PCA applied to the X‐ray fluorescence results revealed a clear cluster separation to the samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative elemental analysis of individual particles with the use of micro‐beam X‐ray fluorescence method and Monte Carlo simulation

The aim of the work was to develop a Monte Carlo (MC) method and combine it with micro‐beam X‐ray fluorescence (XRF) technique for determination of chemical composition of individual particles. A collection of glass micro‐spheres, made of NIST (National Institute of Standards and Technoly) K3089 material of known chemical composition, with diameters in the range of 25–45 µm was investigated. The micro‐spheres were measured in a scanning micro‐beam XRF spectrometer utilising X‐ray tube as a source of primary radiation. Results obtained for low Z elements showed high dependence on particle size. It was found that the root mean square of concentration uncertainty, for the all elements present in the particle, increases with growing sample size. More accurate results were obtained for high Z elements such as Fe–Pb, as compared to others. The elemental percentage uncertainty did not exceed 14% for any particular sample and 6% for the whole group of the measured micro‐spheres as an average. Results obtained by the Monte Carlo method were compared with other analytical approaches. Copyright © 2009 John Wiley & Sons, Ltd.     

The first microbeam synchrotron X‐ray fluorescence beamline at the Siam Photon Laboratory

The first microbeam synchrotron X‐ray fluorescence (µ‐SXRF) beamline using continuous synchrotron radiation from Siam Photon Source has been constructed and commissioned as of August 2011. Utilizing an X‐ray capillary half‐lens allows synchrotron radiation from a 1.4 T bending magnet of the 1.2 GeV electron storage ring to be focused from a few millimeters‐sized beam to a micrometer‐sized beam. This beamline was originally designed for deep X‐ray lithography (DXL) and was one of the first two operational beamlines at this facility. A modification has been carried out to the beamline in order to additionally enable µ‐SXRF and synchrotron X‐ray powder diffraction (SXPD). Modifications included the installation of a new chamber housing a Si(111) crystal to extract 8 keV synchrotron radiation from the white X‐ray beam (for SXPD), a fixed aperture and three gate valves. Two end‐stations incorporating optics and detectors for µ‐SXRF and SXPD have then been installed immediately upstream of the DXL station, with the three techniques sharing available beam time. The µ‐SXRF station utilizes a polycapillary half‐lens for X‐ray focusing. This optic focuses X‐ray white beam from 5 mm × 2 mm (H × V) at the entrance of the lens down to a diameter of 100 µm FWHM measured at a sample position 22 mm (lens focal point) downstream of the lens exit. The end‐station also incorporates an XYZ motorized sample holder with 25 mm travel per axis, a 5× ZEISS microscope objective with 5 mm × 5 mm field of view coupled to a CCD camera looking to the sample, and an AMPTEK single‐element Si (PIN) solid‐state detector for fluorescence detection. A graphic user interface data acquisition program using the LabVIEW platform has also been developed in‐house to generate a series of single‐column data which are compatible with available XRF data‐processing software. Finally, to test the performance of the µ‐SXRF beamline, an elemental surface profile has been obtained for a piece of ancient pottery from the Ban Chiang archaeological site, a UNESCO heritage site. It was found that the newly constructed µ‐SXRF technique was able to clearly distinguish the distribution of different elements on the specimen.     

A pigment (CuS) identified by micro‐Raman spectroscopy on a Chinese funerary lacquer ware of West Han Dynasty

A blue pigment was identified by micro‐Raman spectroscopy, X‐ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX) and X‐ray diffraction (XRD). The test sample, a funerary lacquer tray, belongs to West Han Dynasty (206 BC–AD 8) of China and was decorated with faint blue patterns. The result from Raman spectroscopy showed that the faint blue is covellite (CuS) due to the presence of a characteristic peak at 474.5 cm⁻¹, which further was confirmed by XRF, SEM–EDX and XRD. This research indicated that CuS had been used as a blue pigment to decorate lacquer wares from the West Han Dynasty in China. Copyright © 2009 John Wiley & Sons, Ltd.     

Development of a high‐resolution confocal micro‐XRF instrument equipped with a vacuum chamber

A confocal micro‐X‐ray fluorescence (micro‐XRF) instrument equipped with a vacuum chamber was newly developed. The instrument is operated under a vacuum condition to reduce the absorption of XRF in the atmosphere. Thin metal layers were developed to evaluate the confocal volume, corresponding to depth resolution. A set of thin metal layers (Al, Ti, Cr, Fe, Ni, Cu, Zr, Mo, and Au) was prepared by a magnetron sputtering technique. The depth resolutions of the new instrument were varied from 56.0 to 10.9 µm for an energy range from 1.4 to 17.4 keV, respectively. The lower limit of detection (LLD) was estimated by comparison with a glass standard reference material NIST SRM 621). The LLDs obtained by a conventional micro‐XRF were compared with the LLDs obtained by a confocal micro‐XRF instrument. The LLDs were improved in the measurement under confocal configuration because of the reduction of background intensity. Finally, layered materials related to forensic investigation were measured. The confocal micro‐XRF instrument was able to nondestructively obtain the distribution of light elements that cannot be detected by measurement in air. Copyright © 2013 John Wiley & Sons, Ltd.     

Thickness determination of gold layer on pre‐Columbian objects and a gilding frame,combining pXRF and PLS regression

In conservation, restoration and characterization studies of art and archaeological objects, the improvement of analytical techniques is a tendency. X‐ray fluorescence (XRF) is a versatile technique, and it has been widely used in the last decades for characterization of a great variety of materials (metals, glass, paints, inks, ceramics, etc.) applied to cultural heritage studies. Besides the chemical composition, it is possible to infer the layer thickness through XRF, enabling a general knowledge of the manufacturing techniques implemented by the culture of origin, as well as the association with the technological level reached for the production of each kind of artefact. The aim of this study is to introduce an alternative way for gold thickness determination of coatings in cultural heritage objects, combining portable XRF data and partial least square regression. As a case of study, we present the use of this methodology in portable XRF measurements performed in situ on a gilding frame in Brazil and in two pre‐Columbian artefacts from Chavin culture in Peru. Gold layers with thicknesses determined by Rutherford backscattering spectrometry (RBS) were used as standards to perform a calibration model and to check the methodology before its application to unknown artefacts. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

A miniature X‐ray tube approach to measuring lead in bone using L‐XRF

Using a miniature X‐ray tube and silicon PiN diode detector, an approach to measuring lead (Pb) in bone phantoms was tested. The X‐ray tube was used to excite L‐line X‐ray fluorescence (L‐XRF) of lead in bone phantoms. The bone phantoms were made from plaster of Paris and dosed with varying quantities of lead. Phantoms were made in two sets with different shapes to model different bone surfaces. One set of bone phantoms was circular in cross‐section (2.5‐cm diameter), the other square in cross‐section (2.2 cm × 2.2 cm). Using an irradiation time of 180 s (real time), five trials were run for each bone phantom. Analysis was performed for both Lα and Lβ lead X‐rays. Based on these calibration trials, (3σ₀/slope) minimum detection limits of 7.4 ± 0.3 µg Pb g^?1 (circular cross‐section) and 8.6 ± 0.6 µg Pb g^?1 (square cross‐section) were determined for the bare bone phantoms. To simulate a more realistic in vivo scenario with soft tissue overlying bone, further trials were performed with a resin material placed between the experimental system and the bone phantom. For the square cross‐section bone phantoms, a layer of resin with a thickness of 1.2 mm was used, and a minimum detection limit of 17 ± 3 µg Pb g^?1 determined. For the circular cross‐section phantoms, a layer of resin with an average thickness of 2.7 mm was used. From these, a more realistic minimum detection limit for in vivo applications (43 ± 7 µg Pb g^?1) was determined. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of cobalt marker in cow ruminal fluid by EDXRF and SRTXRF

This article describes a comparison of conventional energy‐dispersive X‐ray fluorescence (EDXRF) and synchrotron radiation total‐reflection X‐ray fluorescence (SRTXRF) for Co determination in ruminal fluid from Holstein cow. This element is used as marker for animal nutrition studies. For EDXRF, 200 µl of the sample were dried on 6.35 µm Mylar film at 60 °C. The excitation was carried out using an X‐ray tube with Mo target and Zr filter operated at 30 kV/20 mA. For SRTXRF, 10 µl of the sample were pipetted on a Lucite carrier and dried at 60 °C. In both the techniques, Ga was used as internal standard and the acquisition time was 200 s. The trueness of both techniques was evaluated through the standard addition method, the recoveries obtained by SRTXRF and EDXRF were 76 and 99%, and the limits of detection, 13 and 240 µg l^?1, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Approaches to solid sample preparation based on analytical depth for reliable X‐ray fluorescence analysis

In this paper, we discuss approaches to prepare solid samples for X‐ray fluorescence spectrometry (XRF). Although XRF can be used to analyze major and minor elements in various solid samples including powders and grains without dissolution techniques, to obtain reliable XRF results, the prepared sample must meet certain criteria related to homogeneity, particle size, flatness, and thickness. The conditions are defined by the analytical depth of fluorescent X‐rays from analytes, and the analytical depth can be estimated from the X‐ray absorption related to the energy of each X‐ray and the composition and density of the sample. For example, when the sample flatness and particle size are less than the analytical depth and the sample possesses homogeneity within a depth less than the analytical depth, the XRF results are representative of the entire sample. Furthermore, an appropriate sample thickness that is larger than the analytical depth or constant can prevent changes in fluorescent X‐ray intensity with variations in sample thickness. To obtain accurate and reproducible measurements, inhomogeneous solid samples must be pulverized, homogenized, and prepared as loose powder, powder pellets, or glass beads. This paper explains the approaches used to prepare solid samples for XRF analysis based on the analytical depths of fluorescent X‐rays. Copyright © 2016 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.     

Identification of pigments from the Shrine of Kaiping Diaolou by micro‐Raman spectroscopy

Shrines (or altars) are constructed in China for worshiping ancestors, Bodhisattva, and God of Wealth. In this work, pigments from the shrine of Kaiping Diaolou tower were analyzed by micro‐Raman spectroscopy, in conjunction with other analytical methods including scanning electron microscopy (SEM) with energy dispersive X‐ray spectroscopy (EDX) and X‐ray fluorescence (XRF). Paintings of the shrine were composed of 2–3 pigment layers and the total thickness was determined as about 200–300 µm by optical microscopy and SEM, indicating the fine painting skills applied in the construction of the shrine. The green pigments on the surface layer of the green fragment were identified as a mixture of lead phthalocyanine (PbPc) and cornwallite (Cu₅(AsO₄)₂(OH)₄) by XRF and micro‐Raman spectroscopy with two different excitation wavelengths (488 and 785 nm). Underneath the green layer, red and yellow ochre were found. The pigments on the surface layer of red and blue fragments were identified as hematite (Fe₂O₃) and lazurite or synthetic ultramarine [(Na₈(Al₆Si₆O₂₄)S₃)], respectively. Finally, the pigments under the two surface layers were identified by EDX and micro‐Raman spectroscopy as chromium oxide (Cr₂O₃), gypsum (CaSO₄·2H₂O) and calcite (CaCO₃). Copyright © 2011 John Wiley & Sons, Ltd.     

Confocal macro X‐ray fluorescence spectrometer on commercial 3D printer

Novel confocal X‐ray fluorescence (XRF) spectrometer was designed and constructed for 3D analysis of elementary composition in the surface layer of spatially extended objects having unlimited chemical composition and geometrical shape. The main elements of the XRF device were mounted on a moving frame of a commercial 3D printer. The XRF unit consists of a silicon drift detector and a low‐power transmission‐type X‐ray tube. Both the excitation and secondary X‐ray beams were formed and regulated by simple collimator systems in order to create a macro confocal measuring setup. The spatial accuracy of the mechanical stages of the 3D printer achieved was less than 5 μm at 100‐μm step‐size. The diameter of the focal spot of the confocal measuring arrangement was between 1.5 and 2.0 mm. The alignment of the excitation and secondary X‐ray beams and the selection of the measuring spot on the sample surface were ensured by two laser beams and a digital microscope for visualization of the irradiated spot. The elements of the optical system together with the XRF spectrometer were mounted on the horizontal arm of the 3D printer, which mechanical design is capable of synchronized moving the full spectroscopic device within vertical directions. Analytical capability and the 3D spatial resolution of the confocal spectrometer were determined. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluation of the concentration of chemical elements in suspended particulate matter inside a small bronze and iron foundry industry,using a streaker sampler and EDXRF

The aim of this study was to determine and evaluate the temporal profiles of the concentration of chemical elements in the suspended particulate matter present inside a small bronze and an iron foundry industry. To collect the samples, we used a streaker sampler that separates particles with aerodynamic diameters smaller than 10 µm (PM₁₀) in two fractions: fine (particles with aerodynamic diameters less than 2.5 µm; PM_2.5) and coarse (between 2.5 µm and less than 10 µm; PM_10–2.5). The collection of samples was taken every 20 min during a total time of 8 and 5 h of molding and casting of bronze and iron, respectively. The samples collected in the form of strips on a filter (fine fraction) and an impactor (coarse fraction) were analyzed by the energy dispersive X‐ray fluorescence technique. In the excitation, an X‐ray tube with Mo target and Zr filter was used, operated at 30 mA/30 kV. For detecting the characteristic of X‐rays, a semiconductor Si(Li) detector was used, coupled to a multi‐channel spectrometer, with a 300 s excitation/detection time. The results of the temporal profiles of chemical element concentrations in coarse and fine fractions were discussed and compared with the maximum levels set by the Brazilian and international environmental agencies. Copyright © 2013 John Wiley & Sons, Ltd.     

Characteristics of a robust and portable large area X‐ray fluorescence imaging system

A low‐cost and portable Energy Disperse X‐Ray Fluorescence imaging system is presented. It is capable of scanning large areas (up to 10 × 10 cm²) in steps as small as 0.2 mm. It consists of a small X‐ray tube and a Silicon Drift Detector, both controlled by a homemade software. The spatial resolution is evaluated as a function of the step width and of the X‐ray collimator diameter. The time of acquisition per unit of scanned surface is studied as a function of the step width and of the time of acquisition per point. X‐ray fluorescence images showing the 2D distributions of some elements in biological samples are presented. Copyright © 2013 John Wiley & Sons, Ltd.