Portable x‐ray fluorescence spectrometer with a pyroelectric x‐ray generator

A portable x‐ray fluorescence spectrometer was assembled with an x‐ray generator that was driven by a 9 V dry electric battery. Several possible optimum geometries of the x‐ray generator and detector were evaluated, and the results showed that the intensity of fluorescent x‐rays was strong enough when the angle between the x‐ray generator and detector was as small as 30°. The geometrically optimized x‐ray spectrometer was applied to the analysis of paints, plastics and aluminum foils. Pigments in paint and toxic elements in plastic could be easily detected with on‐site analysis. Fe in aluminum foil was quantitatively determined down to the sub‐% level. The detection limit of Fe was 180 ppm for 100 s of measurement. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance of polycapillary x‐ray lens for x‐ray sources with various spot sizes

The performance of a polycapillary x‐ray lens (PCXRL) is related to the spot size of the x‐ray source. The transmission efficiency of the PCXRL decreases generally with the increase of the x‐ray source spot size. Both the output focal spot size of a focusing PCXRL and the divergence of a parallel PCXRL increase with increasing source spot size. A large source spot size results in more ‘escape halo’, which affects the measured transmission efficiency and the measured output focal spot size. Copyright © 2007 John Wiley & Sons, Ltd.     

X‐ray fluorescence analysis with a pyroelectric x‐ray generator

Several types of handy x‐ray fluorescence spectrometers are presented. The results obtained with a Niton spectrometer are presented as a goal to develop a laboratory‐made spectrometer using an Amptek Cool‐X pyroelectric x‐ray generator. A small and cheap charge‐up x‐ray emitting device and its spectrum are also presented. Handy x‐ray spectrometers are now progressing rapidly and the detection limits are in the range of a few ppm for certain elements. Copyright © 2005 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.     

Investigation on porosity changes of Lecce stone due to conservation treatments by means of x‐ray nano‐ and improved micro‐computed tomography: preliminary results

Cultural heritage materials are subject to continuous chemical and physical changes depending on the establishment of a dynamic equilibrium with the environment in which they are placed. In particular, different phenomena can take place, such as formation of black crusts, corrosion of the material, internal cracks. Lecce stone, a biocalcarenite mainly used for historical buildings in South Italy, has a high total porosity. In order to prevent its deterioration, different kinds of hydrophobic organic products are applied on the surface of the restored artefacts. Since the efficacy of the treatments depends mostly on the penetration depth and the distribution of the products in the pores, porosity and internal structure of the stone material were mainly investigated in this research. Micro x‐ray computed tomography (µ‐CT) has been used to study and characterize the internal structure of different samples, untreated and treated with protective products. The porosity and other parameters of the rock were then calculated and compared, before and after the conservation treatment, in order to highlight the changes due to the application of the product. On the other hand, small pieces of the untreated and treated samples were analysed by sub‐micron resolution x‐ray tomography where it was possible to see the distribution of the products inside the pores. Copyright © 2007 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.     

Planar waveguide‐resonator: a new device for x‐ray optics

Systematic investigations of the width dependence on the x‐ray beam propagation mechanism for a narrow extended slit formed by two plane dielectric plates are presented. It is shown that the mechanism of a multiple consecutive total reflection for Cu Kα radiation dominates in a slit width range s ≥ 3 µm. At the same time the manner of Cu Kα radiation propagation for super‐narrow slits s ≤ 0.1 µm is very different from the multiple total reflection mechanism. The x‐ray beam intensity proves to be constant for all this range of magnitude. This gives grounds to expect that the super‐narrow slit area is characterized by a specific type of mechanism of x‐ray beam propagation: waveguide‐resonance. A simple model for the waveguide‐resonance propagation mechanism based on the formation of a uniform x‐ray standing wave interference field in the total space of a narrow extended slit was developed. The design of a new x‐ray optical device, namely a planar x‐ray waveguide‐resonator, is proposed based on the waveguide‐resonance mechanism. Some properties of the composite planar x‐ray waveguide‐resonator are discussed. It is shown that under specific conditions the composite waveguide can demonstrate a partial tunneling effect of the x‐ray beam. The main applications of the new technique are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

X‐ray fluorescence computed tomography with absorption correction for biomedical samples

To obtain accurate distributions of trace elements in biomedical samples nondestructively, the problems on absorption correction and radiation dose are confronted in X‐ray fluorescence computed tomography. In this paper, the absorption‐corrected ordered subsets expectation maximization (AC‐OSEM) algorithm is developed to solve these problems. Simulation results show that the AC‐OSEM‐based X‐ray fluorescence computed tomography is accurate when only the incident X‐ray attenuation map is known and relatively fewer projections are provided. In addition, for the biomedical samples, the simplified approximate expression of the fluorescence attenuation map is practicable. Experiments on the biomedical samples were also carried out to evaluate the applicability of the AC‐OSEM algorithm to soft tissues, which demonstrates that the distribution of the trace element Fe in the pathological liver could be clearly revealed. Copyright © 2014 John Wiley & Sons, Ltd.     

Superconducting tunnel junctions as detectors for high‐resolution x‐ray spectroscopy

Superconducting tunnel junctions (STJs) are a type of cryogenic detector with a working temperature of about 100 mK. They allow the combination of low energy threshold, high quantum efficiency and good count rate capability with an excellent energy resolution; at an x‐ray energy of 5.9 keV an energy resolution of 10.8 eV (FWHM) has been achieved. The detector system described is based on STJs which consist of two superconducting Al electrodes separated by a thin dielectric tunnel barrier. The tunneling process of quasi‐particles created by deposition of energy in the electrodes leads to a detectable current signal. The STJ is equipped with a superconducting Pb absorber which is read out via phonons. The Pb absorber increases absorption efficiency (～50% at 6 keV) and suppresses detector artefacts. The degeneration of Pb, most probably due to oxidation, is overcome by the introduction of a protective SiO layer on top of the absorber. This layer leads to a slight reduction of energy resolution. Nevertheless, a resolution of 9.7 eV at 1.7 keV and of ～20 eV at 5.9 keV could be realized with a prototype detector. Currently this STJ‐based detector system is being incorporated into a prototype cryogenic spectrometer for XRF analysis. Copyright © 2004 John Wiley & Sons, Ltd.     

Calculation of the transmission efficiency of a monolithic polycapillary x‐ray lens for an x‐ray source of any shape

A method for calculating the transmission efficiency of a monolithic polycapillary x‐ray lens is presented. Using this method, the transmission efficiency of an x‐ray source of any shape can be calculated by using the transmission efficiency measured with a microfocus x‐ray source. Copyright © 2005 John Wiley & Sons, Ltd.     

X‐ray absorption and x‐ray fluorescence for the characterization of titanium oxide‐modified HPLC silicas

Titanium oxide grafted on to the surfaces of chromatographic silica was investigated by x‐ray fluorescence (XRF) and x‐ray absorption (XAS) spectroscopy and the latter used before and after the extensive use of this material as a support for reversed‐phase high‐performance liquid chromatography (RP‐HPLC). XRF indicated the formation of a complete 2:1 monolayer whereas XAS suggested the presence of more than one titanium oxide structure. These structures show some slight modification after immobilization of PMOS and use in HPLC. Copyright © 2005 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.     

Random left‐censoring: a statistical approach accounting for detection limits in x‐ray fluorescence analysis

The use of x‐ray fluorescence techniques (XRF, TXRF, µXRF) in studies of trace element concentrations is limited by the detection limits (DL) of these methods. In this work we demonstrate that concentration measurements below the DL level, the so‐called ‘non‐detects’, can be included in data analysis by using the statistical concept of ‘censoring’, which is widely used, for instance, in survival analysis. This paper describes the non‐parametric methods of analysis of censored data using the random left‐censoring formalism, which can be used to account for the detection limits in XRF analysis. In particular, the application of the Kaplan–Meier and Nelson–Aalen estimators for the estimation of concentration distributions under censoring is discussed. These approaches are compared with the ‘reconstruction method’ developed earlier in our group to correct XRF data for the effect of detection limits. By using Monte Carlo simulations, the accuracy of the Kaplan–Meier and Nelson–Aalen estimators for censored data is discussed, in particular in the context of the estimation of the mean value and median of a concentration distribution. We demonstrate that for the ‘two‐group’ comparison of left‐censored concentrations, which is a problem of great practical importance, the log‐rank test can be used. The idea of random left censoring is applied to analyse the TXRF detection limit‐censored measurements of the concentrations of trace elements in biomedical samples. Copyright © 2004 John Wiley & Sons, Ltd.     

Micro‐beam x‐ray fluorescence analysis of individual particles with correction for absorption effects

A method of correction for absorption effects in micro‐beam x‐ray fluorescence analysis is described. A fast, energy‐dispersive, silicon drift detector (SDD) was used to measure the primary x‐ray beam transmitted through the sample. The absorption factors were calculated using the data acquired with the SDD. The possibility of using the coherently, incoherently and multiple scattered primary radiation for determining the mass of individual particles was examined. The proposed methods were validated with the use of NIST K3089 glass micro‐spheres of known composition. Copyright © 2006 John Wiley & Sons, Ltd.     

Fast and accurate X‐ray fluorescence computed tomography imaging with the ordered‐subsets expectation maximization algorithm

The ordered‐subsets expectation maximization algorithm (OSEM) is introduced to X‐ray fluorescence computed tomography (XFCT) and studied; here, simulations and experimental results are presented. The simulation results indicate that OSEM is more accurate than the filtered back‐projection algorithm, and it can efficiently suppress the deterioration of image quality within a large range of angular sampling intervals. Experimental results of both an artificial phantom and cirrhotic liver show that with a satisfying image quality the angular sampling interval could be improved to save on the data‐acquisition time when OSEM is employed. In addition, with an optimum number of subsets, the image reconstruction time of OSEM could be reduced to about half of the time required for one subset. Accordingly, it can be concluded that OSEM is a potential method for fast and accurate XFCT imaging.     

Potential of propagation‐based synchrotron X‐ray phase‐contrast computed tomography for cardiac tissue engineering

Hydrogel‐based cardiac tissue engineering offers great promise for myocardial infarction repair. The ability to visualize engineered systems in vivo in animal models is desired to monitor the performance of cardiac constructs. However, due to the low density and weak X‐ray attenuation of hydrogels, conventional radiography and micro‐computed tomography are unable to visualize the hydrogel cardiac constructs upon their implantation, thus limiting their use in animal systems. This paper presents a study on the optimization of synchrotron X‐ray propagation‐based phase‐contrast imaging computed tomography (PCI‐CT) for three‐dimensional (3D) visualization and assessment of the hydrogel cardiac patches. First, alginate hydrogel was 3D‐printed into cardiac patches, with the pores filled by fibrin. The hydrogel patches were then surgically implanted on rat hearts. A week after surgery, the hearts including patches were excised and embedded in a soft‐tissue‐mimicking gel for imaging by using PCI‐CT at an X‐ray energy of 25 keV. During imaging, the sample‐to‐detector distances, CT‐scan time and the region of interest (ROI) were varied and examined for their effects on both imaging quality and radiation dose. The results showed that phase‐retrieved PCI‐CT images provided edge‐enhancement fringes at a sample‐to‐detector distance of 147 cm that enabled visualization of anatomical and microstructural features of the myocardium and the implanted patch in the tissue‐mimicking gel. For visualization of these features, PCI‐CT offered a significantly higher performance than the dual absorption‐phase and clinical magnetic resonance (3 T) imaging techniques. Furthermore, by reducing the total CT‐scan time and ROI, PCI‐CT was examined for lowering the effective dose, meanwhile without much loss of imaging quality. In effect, the higher soft tissue contrast and low‐dose potential of PCI‐CT has been used along with an acceptable overall animal dose to achieve the high spatial resolution needed for cardiac implant visualization. As a result, PCI‐CT at the identified imaging parameters offers great potential for 3D assessment of microstructural features of hydrogel cardiac patches.     

The fractional Fourier transform as a simulation tool for lens‐based X‐ray microscopy

The fractional Fourier transform (FrFT) is introduced as a tool for numerical simulations of X‐ray wavefront propagation. By removing the strict sampling requirements encountered in typical Fourier optics, simulations using the FrFT can be carried out with much decreased detail, allowing, for example, on‐line simulation during experiments. Moreover, the additive index property of the FrFT allows the propagation through multiple optical components to be simulated in a single step, which is particularly useful for compound refractive lenses (CRLs). It is shown that it is possible to model the attenuation from the entire CRL using one or two effective apertures without loss of accuracy, greatly accelerating simulations involving CRLs. To demonstrate the applicability and accuracy of the FrFT, the imaging resolution of a CRL‐based imaging system is estimated, and the FrFT approach is shown to be significantly more precise than comparable approaches using geometrical optics. Secondly, it is shown that extensive FrFT simulations of complex systems involving coherence and/or non‐monochromatic sources can be carried out in minutes. Specifically, the chromatic aberrations as a function of source bandwidth are estimated, and it is found that the geometric optics greatly overestimates the aberration for energy bandwidths of around 1%.     

Composition determination for complex and transmitting samples in x‐ray quantitative analysis

In this work, quantitative analysis of x‐ray fluorescence measurements of transmitting samples with complex chemical composition is considered. A method is presented for analytical solution of sample composition including matrix effects, independent of sample thickness and requiring no standards. The method uses fundamental parameters and measured fluorescence signal intensities, and is applicable to transmission geometry measurements for which standard analyses are not applicable. Limitations of the analysis presented here are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Thin‐film characterization with x‐ray microanalysis. Extending and improving invariant embedding results

Invariant embedding theoretical results for the recorded x‐ray intensities in electron probe microanalysis were used to develop a procedure for thin films. The method presented here gives the possibility of achieving thin‐film characterization directly from characteristic x‐rays intensities measurements, without the necessity to make an explicit calculation of the ?(ρz) function. Theoretical results are found to follow the general trend of experimental data. Copyright © 2003 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.