Full-field X-ray Fluorescence Research Articles

3D printed imaging apertures for MicroPattern gas detector based full field of view X-ray fluorescence spectrometers

Additive Manufacturing, commonly referred as 3D printing, opened a new way to promptly produce cost-effective imaging apertures based on high-density materials, to be used in x-ray imaging systems, such as MicroPattern Gas Detector (MPGD) based Full Field X-ray Fluorescence (FF-XRF) spectrometers. These provide energy and spatially resolved information, allowing the mapping of large area samples. Traditionally, image formation is accomplished with pinhole apertures, devices of easy manufacturing that lead to sub-micrometre position resolution values. However, the sensitivity of the imaging system is severely hampered. To surpass this issue, alternative optical components, such as parallel multi-hole collimators, can be used.In this work, 3D printed multi-hole collimators with different geometries and material compositions are presented and applied to a FF-XRF spectrometer based on the 2D-THCOBRA gas detector. The system's performance parameters with different collimators, namely, relative sensitivity and position resolution, were experimentally determined and compared with the ones obtained with pinhole-based setups. The FF-XRF spectrometer was also simulated, to understand how different collimator geometries affect sensitivity and position resolution.

The study of X-ray full-field imaging method for low atomic number elements based on Compton scattering

Full-field X-ray fluorescence imaging cannot image low atomic number (Z < 12) materials because the characteristic X-ray fluorescence produced by low atomic number (Z < 12) materials is severely attenuated in air. In this paper, we propose a method to combine Compton scattering with full-field X-ray fluorescence imaging, which can realize the imaging of both metals (high atomic number) and organic materials (low atomic number), and compensate the defect that the conventional FF-XRFI technique cannot image materials with low atomic number such as organic materials. The imaging experiments were performed using two materials, zirconium metal and polyethylene, and the imaging results were optimized using a density filtering algorithm, and the results indicate that it is possible to use this method to image samples of high and low atomic number with resolution.

A new full-field XRF imaging station at Synchrotron Light Research Institute.

A full-field X-ray fluorescence imaging (FXI) station was recently developed at beamline BL8 of Synchrotron Light Research Institute (SLRI), Thailand. An unfocused, synchrotron X-ray beam from the bending magnet with a size of 2 mm (vertical) × 13 mm (horizontal) and photon energy of 10 keV was employed in the FXI experiments. A sample stage was tilted by 7.5° to enlarge the vertical beam size. X-ray fluorescence images were recorded by an energy-dispersive, 256 × 256 array, pn-type charge coupled device detector equipped with a polycapillary optics, providing a full-frame image size of 12.3 mm × 12.3 mm. The incident photon flux per pixel was 3 × 104 photons s-1 (100 mA)-1 and the experimental spatial resolution was 68 µm. Image processing was carried out offline using an in-house MATLAB program capable of elemental selection and inhomogeneity intensity correction. Elemental detection limits of FXI were found to decrease with increasing atomic number, i.e. 0.3 to 0.03 wt% for Z = 19 (K) to 30 (Zn). Compared with the BL6b microbeam imaging (µXI) station at SLRI with higher photon flux per pixel, 3 × 1010 photons s-1 (100 mA)-1, a tenfold sample area can be obtained and 13 times higher peak-to-background (PKB) ratio at Zn Kα measured with the same experimental time (8 h). Simultaneous measurement of FXI is more time-efficient against the long overhead times of µXI scanning over large pixel numbers, >65000. To demonstrate potential applications of the new FXI station, various types of samples were examined: dendritic limestone, ancient bronze and dried fish. Analyzed elemental images enabled us to identify areas rich in Mn on the limestone, Sn and Cu separation in the bronze, and Zn nutrition in the dried fish eye.

Full-field x-ray fluorescence imaging using a Fresnel zone plate coded aperture

We present an approach to full-field x-ray fluorescence imaging that uses a Fresnel zone plate as a coded aperture positioned between the object and detector. For this particular coded aperture, the incoherent image formation is identical to the coherent propagation image (inline hologram) of an equivalent absorption object. In the first experiment, we show that prior knowledge of the coded aperture structure and position is no longer required. Fast and robust reconstruction algorithms well known from coherent imaging can be applied. We demonstrate the approach using x-ray fluorescence excited by a collimated Cu- K α beam at an ordinary laboratory x-ray source. Images are recorded with a field of view of 1 m m 2 and resolution of 35 µm. The simple and efficient imaging scheme is well suited for further dissemination of x-ray fluorescence imaging and translation to a broader user community, which could take advantage of full-field imaging with chemical contrast. More generally, the scheme also enables full-field imaging of other incoherent radiation processes for which lenses are either not available at all or not with sufficient numerical apertures. Examples include Compton imaging, imaging of inelastic neutron scattering, or γ -ray imaging in nuclear medicine.

Characterization of micro pore optics for full-field X-ray fluorescence imaging

Elemental mapping images can be achieved through step scanning imaging using pinhole optics or micro pore optics (MPO), or alternatively by full-field X-ray fluorescence imaging (FF-XRF). X-ray optics for FF-XRF can be manufactured with different micro-channel geometries such as square, hexagonal or circular channels. Each optic geometry creates different imaging artefacts. Square-channel MPOs generate a high intensity central spot due to two reflections via orthogonal channel walls inside a single channel, which is the desirable part for image formation, and two perpendicular lines forming a cross due to reflections in one plane only. Thus, we have studied the performance of a square-channel MPO in an FF-XRF imaging system. The setup consists of a commercially available MPO provided by Photonis and a Timepix3 readout chip with a silicon detector. Imaging of fluorescence from small metal particles has been used to obtain the point spread function (PSF) characteristics. The transmission through MPO channels and variation of the critical reflection angle are characterized by measurements of fluorescence from copper and titanium metal fragments. Since the critical angle of reflection is energy dependent, the cross-arm artefacts will affect the resolution differently for different fluorescence energies. It is possible to identify metal fragments due to the form of the PSF function. The PSF function can be further characterized using a Fourier transform to suppress diffuse background signals in the image.

Application of Factorisation Methods to Analysis of Elemental Distribution Maps Acquired with a Full-Field XRF Imaging Spectrometer

The goal of the work was to investigate the possible application of factor analysis methods for processing X-ray Fluorescence (XRF) data acquired with a full-field XRF spectrometer employing a position-sensitive and energy-dispersive Gas Electron Multiplier (GEM) detector, which provides only limited energy resolution at a level of 18% Full Width at Half Maximum (FWHM) at 5.9 keV. In this article, we present the design and performance of the full-field imaging spectrometer and the results of case studies performed using the developed instrument. The XRF imaging data collected for two historical paintings are presented along with the procedures applied to data calibration and analysis. The maps of elemental distributions were built using three different analysis methods: Region of Interest (ROI), Non-Negative Matrix Factorisation (NMF), and Principal Component Analysis (PCA). The results obtained for these paintings show that the factor analysis methods NMF and PCA provide significant enhancement of selectivity of the elemental analysis in case of limited energy resolution of the spectrometer.

Characterization of a large-area full-field X-ray fluorescence imaging system based on a commercial full-frame CMOS camera

A new large-area and low-cost full-field X-ray fluorescence imaging system was developed for simultaneous mapping of several chemical elements. It consists of a commercially available full-frame visible-light CMOS digital camera coupled to a tungsten pinhole-collimator. The X-ray fluorescence is produced by irradiating the sample with an external X-ray tube. The system magnification can be continuously adjusted from 0.55 to 1.43 by changing the position of the pinhole in the collimator. To allow X-ray sensitivity, the glass window of the CMOS sensor was removed and the front glass cover of the camera was replaced by an X-ray window. The x-ray spectra and 2D X-ray fluorescence images of different elements are obtained by processing a series of images acquired in a spectroscopy mode using the CMOS camera. The camera is able to resolve fluorescence lines up to 22 keV, with an energy resolution of 213 eV at 6.4 keV. The experimental spatial resolution is 105 μm when using a 90 μm pinhole at 1.43× magnification. The capabilities of the system in performing the 2D resolved X-ray fluorescence imaging were investigated by testing samples of different materials and geometries. The obtained X-ray fluorescence spectra and images show that the system is able to accurately identify the presence of several different elements and visualize their spatial distributions.

Elemental mapping of Portuguese ceramic pieces with a full-field XRF scanner based on a 2D-THCOBRA detector

In this work, we present a novel application of the full-field energy-dispersive X-ray fluorescence (EDXRF) imaging system based on a MicroPattern Gaseous Detector (2D-THCOBRA) in the cultural heritage field. The detector has an intrinsic imaging capability with spatial resolution of $$400\,{\upmu }\mathrm { m}\ \mathrm {FWHM}$$ , and is energy sensitive, presenting an energy resolution of approximately $$1\ \mathrm {keV\ FWHM}$$ at $$5.9\ \mathrm {keV}$$ . The full-field XRF scanner based on the 2D-THCOBRA detector allows mapping the distribution of elements in large area samples with high detection efficiency ( $$75\%$$ at $$5.9\ \mathrm {keV}$$ ), being a very promising choice for elemental mapping analysis of large area cultural heritage samples. In this work, we have demonstrated the imaging capabilities of the full-field XRF scanner and used it to assess the restoration of a Portuguese faience piece.

Equipment design and performance characterization of full field x-ray fluorescence (FF-XRF) element distribution imaging system with combined collimating lens (CCL).

This work describes a full field x-ray fluorescence element distribution imaging system with a combined collimating lens (CCL), which is more suitable for a higher x-ray energy range (12 keV-30 keV). The system consists of an optical-use charge-coupled device (CCD) camera coupled to a combined collimating lens (CCL), which includes pinhole collimator and x-ray window, x-ray tube, and sample room. The continuously variable magnification of 0.5-2 is achieved under a compact structure. The x-ray spectrum and two-dimensional element distribution mapping of the irradiated sample are obtained by processing a series of images acquired by using the CCD camera in a single photon counting mode. The energy resolution is 275 eV at the reference energy of 14.957 keV (yttrium Kα, Z = 39). The limit of detection is 46.41 ppm by measuring yttrium standard solution. The spatial resolution is 135 μm when using a 100 μm pinhole at the magnification of 1. Samples made by metal foils and mineral pigments are tested, and the results proved that the system was reliable when detecting elements of a high atomic number.

Full-field X-ray fluorescence imaging with a straight polycapillary X-ray collimator

Due to the availability of X-ray imaging detectors, full-field X-ray fluorescence (FF-XRF) imaging technique has become achievable, which provides an alternative to scanning X-ray fluorescence imaging with a micro-focus X-ray beamline. In this paper, we present a setup based on straight capillary optics and an energy-dispersive hybrid pixel detector, which can perform simultaneous mapping of several chemical elements. The photon transmission efficiency and spatial resolution are compared between two X-ray collimation setups: one using pinhole optics and one using straight polycapillary optics. There is a tradeoff between the spatial resolution and transmission efficiency when considering X-ray optics. When optimizing the spatial resolution, using straight capillary optics achieved a higher intensity gain when comparing with the pinhole setup. Characterization of the polycapillary imaging setup is performed through analyzing various samples in order to investigate the spatial frequency response and the energy sensitivity. This developed setup is capable of FF-XRF imaging in characteristic energies below 20 keV, while for higher energies the spatial resolution is affected by photon transmission through the collimator. This work shows the potential of the FF-XRF instrument in the monitoring of toxic metal distributions in environmental mapping measurements.

Modelling of vignetting effects in full-field X-ray fluorescence imaging system based on pinhole optics

The full field X-ray fluorescence (FF-XRF) imaging is a technique capable of analysing the spatial distribution of elements in a sample. An alternative technique is the scanning macro-XRF method. Both techniques are powerful tools for non-destructive analysis of artworks mainly historical paintings. Technically, FF-XRF imaging is usually realised by coupling of a pinhole camera and a position sensitive and energy dispersive X-ray detector. The main advantages of the pinhole camera are its simplicity and infinite depth of field, however it introduces vignetting. For a visible light pinhole camera one distinguishes natural vignetting following the cos4 law and mechanical vignetting due to finite thickness of the camera. For an X-ray pinhole camera one has to take into account an additional component of vignetting due to absorption of X-rays in the air or other gas unless the setup is kept in vacuum. The goal of this study is to work out an analytical model of vignetting effects for a FF-XRF apparatus using an X-ray pinhole camera. Complete quantitative characterisation of the vignetting effects is a key step towards proper correction of the vignetting artefacts in recorded images. The elaborated analytical model has been applied to the images acquired with the FF-XRF apparatus being developed and an example of vignetting correction is presented.

IAEA Nuclear Science and Instrumentation Laboratory: Support to IAEA Member States and Recent Developments

As part of the International Atomic Energy Agency's (IAEA) Physics Section, the Nuclear Science and Instrumentation Laboratory (NSIL) helps Member States (MSs) to establish, operate and maintain various nuclear instrumentation and spectrometry techniques in support of a wide range of applications such as health care, food, agriculture, environment, forensics, cultural heritage, and materials science. NSIL is contributing to capacity building, transfer of knowledge and expertise sharing, including the development of instruments and validation of analytical methodologies. This paper describes NSIL's key activities and provides an overview of the recent developments and achievements, including the commissioning and utilization of an end-station at one of the beam lines in Elettra Sincrotrone Trieste (EST, Italy), the upgrade of an ultralight radiation monitoring system onboarded on a drone, as well as the development of a full field X-ray fluorescence analytical system for forensic applications and characterization of valuable art/archaeological objects.

On the way to full-field X-ray fluorescence spectroscopy imaging with coded apertures

The new reconstruction algorithms for near-field coded aperture imaging show a good performance even in cases where the established method by convolution fails, thus providing a basis for a new approach to full-field X-ray fluorescence imaging.

Expanding a polarized synchrotron beam for full-field x-ray fluorescence imaging.

Full-field x-ray fluorescence (XRF) imaging is an efficient technique for investigating element composition of a sample and the corresponding spatial distribution. Eliminating scattering x-rays is important for visualizing diluted/trace elements clearly. However, using the linear polarization of synchrotron radiation to remove scattering in full-field XRF imaging has not been feasible for many years because a synchrotron beam is inherently narrow in the direction perpendicular to the polarization and a large imaging area and a low scattering background cannot be simultaneously achieved. In this study, the trade-off was solved by expanding a synchrotron beam in the direction perpendicular to the polarization using an asymmetric-cut Si crystal. Large areas of samples were illuminated. In addition, a collimator plate, which only transmitted scattering x-rays that spread in the polarization direction, was used for imaging. Therefore, the detected scattering intensity was low. The present full-field XRF imaging scheme with a size-expanded polarized synchrotron beam is well suited for visualizing diluted/trace elements. It could be extended to x-ray absorption edge fine structure imaging for analyzing the chemical state of diluted/trace elements in inhomogeneous samples.

Full-field X-ray fluorescence microscope based on total-reflection advanced Kirkpatrick-Baez mirror optics.

A novel full-field X-ray fluorescence microscope based on total-reflection advanced Kirkpatrick-Baez mirror optics was developed. The total-reflection imaging mirror optics arrangement, with four reflections, has the advantage of being able to function both as a powerful low-pass energy filter, completely rejecting incident excitation X-rays, and as an achromatic optical imaging system. Isolated X-ray fluorescence signals can be imaged, avoiding imaging-detector saturation, with low background noise. A prototype fluorescence microscope constructed at SPring-8 demonstrated the capability to simultaneously image elemental distributions using various X-ray fluorescence signals (Ni, Cu, Zn, Ge, and Bi). A half-period spatial resolution of ~0.5-1 µm (1000-500 LP/mm) was achieved, owing to the achromaticity of the imaging mirrors and the photon-counting scheme of the CCD camera used for fluorescence detection.

X-ray standing wave technique with spatial resolution: In-plane characterization of surfaces and interfaces by full-field x-ray fluorescence imaging

The present paper describes a powerful extension of the x-ray standing-wave technique that combines it with the capability of full-field x-ray fluorescence imaging, so that the impurity depth profiles at all different parts of a nanolayer material can be measured in parallel. The imaging capability improves the robustness and reliability of the x-ray standing-wave technique in investigating inhomogeneous two-dimensional materials and soft interfaces. It can also visualize the three-dimensional element-specific structure at a buried interface with a depth resolution at the nanometer level.

Scanning and Full Field X-Ray Fluorescence Imaging with Laboratory X-ray Source

Scanning and Full Field X-Ray Fluorescence Imaging with Laboratory X-ray Source

X-ray fluorescence imaging

Over the past two decades, numerous X-ray micro-beam studies have been published addressing the nondestructive investigation of chemical element distribution in condensed heterogeneous media. Based on this literature, some aspects of the field are discussed in this paper, including X-ray focusing methods and various elemental imaging techniques: scanning and confocal X-ray fluorescence microscopy, full-field X-ray fluorescence microscopy, X-ray fluorescence tomography, and prospects for combining X-ray fluorescence imaging with other physical methods rested on using synchrotron radiation.

ARTROC—a readout ASIC for GEM-based full-field XRF imaging system

In the paper we report on development of an Application Specific Integrated Circuit (ASIC), called ARTROC, being part of a full-field X-ray fluorescence spectroscopy (XRF) imaging system equipped with a standard three stage Gas Electron Multiplier (GEM) detector of 10×10 cm2 area. The ARTROC consists of 64 independent channels, allowing for simultaneous recording of the amplitudes (energy sub-channel) and time stamps (timing sub-channel) of incoming signals. Thanks to the implemented token-based read out of derandomizing buffers, the ASIC also provides data sparsification and full zero suppression. Reconstruction of the hit positions is performed in an external data acquisition system by matching the time stamps of signals recorded in X- and Y-strips. The amplitude information is used for centre of gravity finding in clusters of signals on neighbouring strips belonging to the same detection events. The ASIC could work in one of six gain modes and one of two speed modes. In a slower mode the maximum count rate per channel is 105/s while in a faster mode it is three times higher. The ARTROC comprises also input protection circuits against possible random discharges inside active detector volume, so it can be used without any additional input components. The ASIC has been designed in 350 nm CMOS process. The basic functionality and parameters have been evaluated using the testability functions implemented in the ASIC design. The ASIC has been also tested in a fully equipped GEM detector set-up with X-rays source.

Full-field fan-beam x-ray fluorescence computed tomography system design with linear-array detectors and pinhole collimation: a rapid Monte Carlo study

We present the design concept and initial simulations for a polychromatic full-field fan-beam x-ray fluorescence computed tomography (XFCT) device with pinhole collimators and linear-array photon counting detectors. The phantom is irradiated by a fan-beam polychromatic x-ray source filtered by copper. Fluorescent photons are stimulated and then collected by two linear-array photon counting detectors with pinhole collimators. The Compton scatter correction and the attenuation correction are applied in the data processing, and the maximum-likelihood expectation maximization algorithm is applied for the image reconstruction of XFCT. The physical modeling of the XFCT imaging system was described, and a set of rapid Monte Carlo simulations was carried out to examine the feasibility and sensitivity of the XFCT system. Different concentrations of gadolinium (Gd) and gold (Au) solutions were used as contrast agents in simulations. Results show that 0.04% of Gd and 0.065% of Au can be well reconstructed with the full scan time set at 6 min. Compared with using the XFCT system with a pencil-beam source or a single-pixel detector, using a full-field fan-beam XFCT device with linear-array detectors results in significant scanning time reduction and may satisfy requirements of rapid imaging, such as in vivo imaging experiments.