X-ray Area Detector Research Articles

A charged particle veto detector for kaonic deuterium measurements at DAΦNE

The antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. In this context, the importance of kaonic deuterium x-ray spectroscopy has been well recognized, but no experimental results have yet been obtained due to the difficulty of the measurement. To measure the shift and width of the kaonic deuterium 1s state with an accuracy of 30 eV and 75 eV, respectively, an apparatus is under construction at the Laboratori Nazionali di Frascati. A detailed Monte Carlo simulation has shown that an increase of the signal to background ratio by a factor of ten will be required compared to the successfully performed kaonic hydrogen measurement (SIDDHARTA). Three pillars are essential for the newly developed experimental apparatus: a large area x-ray detector system (consisting of Silicon Drift Detectors), a lightweight cryogenic target system and a veto system, consisting of an outer veto detector (Veto-1) for active shielding and an inner veto detector (Veto-2) for charged particle suppression. For both veto systems, an excellent time resolution is required to distinguish kaons stopping in gas from direct kaon stops in the entrance window or side wall of the target. First test measurements on the Veto-2 system were performed. An average time resolution of (54 ± 2) ps and detection efficiencies of ~ 99 % were achieved.

Macroscopic X-ray Powder Diffraction Scanning, a New Method for Highly Selective Chemical Imaging of Works of Art: Instrument Optimization.

In the past decade macroscopic X-ray fluorescence imaging (MA-XRF) has become established as a method for the noninvasive investigation of flat painted surfaces, yielding large scale elemental maps. MA-XRF is limited by a lack of specificity, only allowing for indirect pigment identification based on the simultaneous presence of chemical elements. The high specificity of X-ray powder diffraction (XRPD) mapping is already being exploited at synchrotron facilities for investigations at the (sub)microscopic scale, but the technique has not yet been employed using lab sources. In this paper we present the development of a novel MA-XRPD/XRF instrument based on a laboratory X-ray source. Several combinations of X-ray sources and area detectors are evaluated in terms of their spatial and angular resolution and their sensitivity. The highly specific imaging capability of the combined MA-XRPD/XRF instrument is demonstrated on a 15th/16th century illuminated manuscript directly revealing the distribution of a large number of inorganic pigments, including the uncommon yellow pigment massicot ( o-PbO). The case study illustrates the wealth of new mapping information that can be obtained in a noninvasive manner using the laboratory MA-XRPD/XRF instrument.

Simultaneous X-ray diffraction, crystallography and fluorescence mapping using the Maia detector

Interactions between neighboring grains influence the macroscale behavior of polycrystalline materials, particularly their deformation behavior, damage initiation and propagation mechanisms. However, mapping all of the critical material properties normally requires that several independent measurements are performed. Here we report the first grain mapping of a polycrystalline foil using a pixelated energy-dispersive X-ray area detector, simultaneously measuring X-ray fluorescence and diffraction with the Maia detector in order to determine grain orientation and estimate lattice strain. These results demonstrate the potential of the next generation of X-ray area detectors for materials characterization. By scanning the incident X-ray energy we investigate these detectors as a complete solution for simultaneously mapping the crystallographic and chemical properties of the sample. The extension of these techniques to broadband X-ray sources is also discussed.

Polycrystalline materials analysis using the Maia pixelated energy-dispersive X-ray area detector

Elemental, chemical, and structural analysis of polycrystalline materials at the micron scale is frequently carried out using microfocused synchrotron X-ray beams, sometimes on multiple instruments. The Maia pixelated energy-dispersive X-ray area detector enables the simultaneous collection of X-ray fluorescence (XRF) and diffraction because of the relatively large solid angle and number of pixels when compared with other systems. The large solid angle also permits extraction of surface topography because of changes in self-absorption. This work demonstrates the capability of the Maia detector for simultaneous measurement of XRF and diffraction for mapping the short- and long-range order across the grain structure in a Ni polycrystalline foil.

Non-uniform nanosecond gate-delay of hybrid pixeldetectors.

A simple experiment to characterize the gating properties of X-ray area detectors using pulsed X-ray sources is presented. For a number of time-resolved experiments the gating uniformity of area detectors is important. Relative gating delays between individual modules and readout chips of PILATUS2series area X-ray detectors have been observed. For three modules of a PILATUS 300K-W unit the maximum gating offset between the modules is found to be as large as 30 ns. On average, the first photosensor module is found to be triggered 15 ns and 30 ns later than the second and the third modules, respectively.

Proposal for a direct-method for stress measurement using an X-ray area detector

The cosα method and the 2D method are well known as X-ray stress measurements using an area detector. Although the X-ray exposure of the cosα method occurs once, the accuracy of the center of the detector is required due to usage of the oblique incident X-ray beam. In the 2D method, the X-ray beams have to be applied from multiple orientations, and multiple measurements are required.In this study, I propose a new method for X-ray stress measurement using an area detector. Its method is called the direct-method”. The diffraction angles are measured with the area detector and the normal incident X-ray beam, and then the stresses are optimized by a simplex method. To examine effectiveness of the direct-method, I measured the residual stresses caused by water-jet peening. The stresses obtained were close to those obtained by the other method. It is discussed that precision of a detector center is important in usage of the area detector. In the case of the normal incident X-ray beam, the shape of the diffraction ring is an ellipse and has point symmetry at the origin. Using this property, the center of the area detector can be corrected. Further, the direct-method was applied to measuring the residual stresses coming from the grinding process. After correcting the center of the diffraction ring, the stresses which were optimized by the simplex method corresponded to those measured by the sin2ψ method. In addition, the direct-method was extended to a cosα method.

In-house time-resolved photocrystallography on the millisecond timescale using a gated X-ray hybrid pixel area detector.

With the remarkable progress of accelerator-based X-ray sources in terms of intensity and brightness, the investigation of structural dynamics from time-resolved X-ray diffraction methods is becoming widespread in chemistry, biochemistry and materials science applications. Diffraction patterns can now be measured down to the femtosecond time-scale using X-ray free electron lasers or table-top laser plasma X-ray sources. On the other hand, the recent developments in photon counting X-ray area detectors offer new opportunities for time-resolved crystallography. Taking advantage of the fast read-out, the internal stacking of recorded images, and the gating possibilities (electronic shutter) of the XPAD hybrid pixel detector, we implemented a laboratory X-ray diffractometer for time-resolved single-crystal X-ray diffraction after pulsed laser excitation, combined with transient optical absorption measurement. The experimental method and instrumental setup are described in detail, and validated using the photoinduced nitrosyl linkage isomerism of sodium nitroprusside, Na2[Fe(CN)5NO]·2H2O, as proof of principle. Light-induced Bragg intensity relative variations ΔI(hkl)/I(hkl) of the order of 1%, due to the photoswitching of the NO ligand, could be detected with a 6 ms acquisition window. The capabilities of such a laboratory time-resolved experiment are critically evaluated.

Development of X-ray CCD camera based X-ray micro-CT system.

Availability of microfocus X-ray sources and high resolution X-ray area detectors has made it possible for high resolution microtomography studies to be performed outside the purview of synchrotron. In this paper, we present the work towards the use of an external shutter on a high resolution microtomography system using X-ray CCD camera as a detector. During micro computed tomography experiments, the X-ray source is continuously ON and owing to the readout mechanism of the CCD detector electronics, the detector registers photons reaching it during the read-out period too. This introduces a shadow like pattern in the image known as smear whose direction is defined by the vertical shift register. To resolve this issue, the developed system has been incorporated with a synchronized shutter just in front of the X-ray source. This is positioned in the X-ray beam path during the image readout period and out of the beam path during the image acquisition period. This technique has resulted in improved data quality and hence the same is reflected in the reconstructed images.

Yoneda-XAFS with Area X-Ray Detectors

ReflXAFS is a well-known, surface sensitive method to investigate the structure of e.g. thin films. By a proper choice of incident and exit angles the Yoneda-peak, a distinct intensity maximum in the diffuse scattering, becomes visible. For multilayered samples, several Yoneda-peaks related to surface and interface regions may be observed. It is possible to utilize these peaks to measure the fine structure of an element inside the related surface and interface regions of a multi-layered sample. We will show that the use of 2D-area detectors allow the simultaneous measurement of the entire scattering pattern for each energy in an EXAFS spectrum, providing access to detailed in-situ structure information of the surface and interface regions in multilayered samples.

X-ray imaging using the thermoluminescent properties of commercial Al2O3 ceramic plates

This research demonstrated that commercially available alumina is well-suited for use in large area X-ray detectors. We discovered a new radiation imaging device that has a high spatial resolution, high sensitivity, wide dynamic range, large imaging area, repeatable results, and low operating costs. The high thermoluminescent (TL) properties of Al2O3 ceramic plates make them useful for X-ray imaging devices.

Phase and strain mapping of a protective coating on carbon–carbon

Abstract Carbon–carbon (C/C) is used in high temperature structures. To prevent rapid oxidation of the carbon, protective coatings are applied. This paper examines such a protective coating with high energy X-ray diffraction. The coating consisted of a 0.02 mm outer layer of sodium silicate glass on a 0.2 mm layer of silicon carbide (SiC) with a 0.1 mm transition layer into the C/C of carbon fibres surrounded by a SiC matrix. It was examined in its pristine state and after heating with an oxy-acetylene torch. An area X-ray detector was used to obtain phase and strain information as a function of depth through the coating. In-plane tensile strains were observed in both a crystalline SiO2 phase and within the SiC of the transition layer. Oxidation protection was compromised by through-thickness cracks in the SiC layer caused by the large tensile cooling strains in the layer. The strains and the density of the cracking increased after heating. However, several mechanisms were identified that moderated the strains. Based on two of these mechanisms a buffer layer of graphite between the C/C and the SiC was proposed to improve oxidation resistance. The low elastic modulus of the graphite reduces the strains in the SiC coating, which reduces the crack density, which in turn improves oxidation resistance. Adding SiC fibres to the graphite and SiC was also proposed to further reduce cracking.

Characterization of hemispherical area X-ray detector based on set of proportional counters with needle anodes

This work introduces a new, versatile and robust X-ray detector with hemispherical 2π geometry, based on a set of 15 small cylindrical proportional counters located in a hexagonal and pentagonal fullerene C60 pattern, at the same distance from the center (where a sample is placed). The counteranode consists of stainless steel sewing needles with spherical tips measuring approximately 80μm in diameter. The space between the counters and the sample could contain air, the same gas as the counters or vacuum. This allows a significant increase in the count rates by a factor approximately equal to the number of counters connected. It is shown that an energy resolution of 20% for 5.9keV photons can be obtained, and a global counting rate of around 106counts/s is achievable by the 15 Needle Anode Proportional Counters (NAPCs) operating in parallel mode, in our setup.

A versatile x-ray microtomography station for biomedical imaging and materials research.

An x-ray microtomography station implemented at the X-ray Applied Crystallography Laboratory of the State University of Campinas is described. The station is based on a propagation based phase contrast imaging setup with a microfocus source and digital x-ray area detectors. Due to its simplicity, this setup is ideal for fast, high resolution imaging and microtomography of small biological specimens and materials research samples. It can also be coupled to gratings to use and develop new techniques as the harmonic spatial coherent imaging, which allow scattering contrast imaging. Details of the experimental setup, equipment, and software integration are described. Test microtomography for setup commissioning and characterization is shown. We conclude that phase contrast enhanced x-ray imaging and microtomography with resolution below 5 μm voxel size are possible and data sets as wide as 2000 × 2000 × 2000 voxels are obtained with this instrumentation.

Performance of low-cost X-ray area detectors with consumer digital cameras

We constructed X-ray detectors using consumer-grade digital cameras coupled to commercial X-ray phosphors. Several detector configurations were tested against the Varian PaxScan 3024M (Varian 3024M) digital flat panel detector. These include consumer cameras (Nikon D800, Nikon D700, and Nikon D3X) coupled to a green emission phosphor in a back-lit, normal incidence geometry, and in a front-lit, oblique incidence geometry. We used the photon transfer method to evaluate detector sensitivity and dark noise, and the edge test method to evaluate their spatial resolution. The essential specifications provided by our evaluation include discrete charge events captured per mm2 per unit exposure surface dose, dark noise in equivalents of charge events per pixel, and spatial resolution in terms of the full width at half maximum (FWHM) of the detector`s line spread function (LSF). Measurements were performed using a tungsten anode X-ray tube at 50 kVp. The results show that the home-built detectors provide better sensitivity and lower noise than the commercial flat panel detector, and some have better spatial resolution. The trade-off is substantially smaller imaging areas. Given their much lower costs, these home-built detectors are attractive options for prototype development of low-dose imaging applications.

Charge transfer inefficiency in the pre- and post-irradiated Swept Charge Device CCD236

This paper describes the mapping of spectral response of an e2v technologies Swept Charge Device (SCD) CCD236 pre and post irradiation with a 10 MeV equivalent proton fluence of 5.0 × 108 protons cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector which will be used in India's Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) and China's Hard X-ray Modulation Telescope (HXMT). To enable the suppression of surface dark current, clocking is performed continuously resulting in a linear readout. As such the flat field illumination used to measure any change in spectral response over a conventional Charge-Coupled Devices (CCDs) is not possible. An alternative masking technique has been used to expose pinpoint regions of the device to Mn-Kα and Mn-Kβ X-rays, enabling a local map of spectral response to be built up over the device. This novel approach allows for an estimation of the Charge Transfer Inefficiency (CTI) of the device to be made by allowing the creation of a CTI scatter plot similar to that typically observed in conventional CCDs.

Imaging single cells in a beam of live cyanobacteria with an X-ray laser.

There exists a conspicuous gap of knowledge about the organization of life at mesoscopic levels. Ultra-fast coherent diffractive imaging with X-ray free-electron lasers can probe structures at the relevant length scales and may reach sub-nanometer resolution on micron-sized living cells. Here we show that we can introduce a beam of aerosolised cyanobacteria into the focus of the Linac Coherent Light Source and record diffraction patterns from individual living cells at very low noise levels and at high hit ratios. We obtain two-dimensional projection images directly from the diffraction patterns, and present the results as synthetic X-ray Nomarski images calculated from the complex-valued reconstructions. We further demonstrate that it is possible to record diffraction data to nanometer resolution on live cells with X-ray lasers. Extension to sub-nanometer resolution is within reach, although improvements in pulse parameters and X-ray area detectors will be necessary to unlock this potential.

Proton irradiation of a swept charge device at cryogenic temperature and the subsequent annealing

A number of studies have demonstrated that a room temperature proton irradiation may not be sufficient to provide an accurate estimation of the impact of the space radiation environment on detector performance. This is a result of the relationship between defect mobility and temperature, causing the performance to vary subject to the temperature history of the device from the point at which it was irradiated. Results measured using Charge Coupled Devices (CCD) irradiated at room temperature therefore tend to differ from those taken when the device was irradiated at a cryogenic temperature, more appropriate considering the operating conditions in space, impacting the prediction of in-flight performance. This paper describes the cryogenic irradiation, and subsequent annealing of an e2v technologies Swept Charge Device (SCD) CCD236 irradiated at −35.4°C with a 10 MeV equivalent proton fluence of 5.0 × 108 protons · cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector that will be flown on-board the Chandrayaan-2 and Hard X-ray Modulation Telescope spacecraft, in the Chandrayaan-2 Large Area Soft X-ray Spectrometer and the Soft X-ray Detector respectively. The SCD is readout continually in order to benefit from intrinsic dither mode clocking, leading to suppression of the surface component of the dark current and allowing the detector to be operated at warmer temperatures than a conventional CCD. The SCD is therefore an excellent choice to test and demonstrate the variation in the impact of irradiation at cryogenic temperatures in comparison to a more typical room temperature irradiation.

Note: A novel normalization scheme for laser-based plasma x-ray sources.

A kHz repetition rate laser pump-X-ray probe system for ultrafast X-ray diffraction is set up based on a laser-driven plasma X-ray source. A simple and reliable normalization approach has been developed to minimize the impact of large X-ray pulse intensity fluctuation on data quality. It utilizes one single X-ray area detector to record both sample and reference signals simultaneously. Performance of this novel normalization method is demonstrated in reflectivity oscillation measurement of a superlattice sample at sub-ps resolution.

Strain And Symmetry-induced Structural Transitions in Ultra-thin BiFeO3 Films

As one of very few room temperature multiferroic materials, bismuth ferrite (BiFeO3: BFO) has been studied extensively in recent years. The bulk form of BFO is known to have a rhombohedrally distorted quasi-cubic perovskite structure with an (a–,a–,a–) octahedral tilt pattern, exhibiting both anti-ferrodistortive displacements and a spontaneous polarization along the <111> axes. Investigating epitaxial thin films under compressive strain, several studies have reported that the polarization direction is tilted towards the [001] out-of-plane direction, while maintaining a significant in-plane component. This effect is accompanied by a significant enhancement of the spontaneous polarization and a series of phase transitions from rhombohedral (R) for small strains to R-like monoclinic (MA) to T-like monoclinic (MC) and to tetragonal (T) for larger strains [1]. Through synchrotron-based 3-dimensional reciprocal space mapping (RSM), facilitated by using X-ray area detectors (Pilatus 100K pixel detector), we have investigated the structure of ultra-thin BFO films grown on SrTiO3 (STO), LaAlO3 (LAO), and TbScO3 (TSO) substrates with thicknesses of only several unit cells. In this thickness regime, the influence of the substrate atomic structure on the properties of the ultra-thin films is very pronounced, and the films exhibit perfect heteroepitaxy up to a critical thickness when the build up of strain energy forces the films into a relaxed structure. Both on STO [2] and LAO, the ultra-thin BFO undergoes a monoclinic to tetragonal phase transition, but with very different c/a axis ratios. On TSO, a very pronounced and well-ordered stripe domainstructure evolves where the domain sizes are strongly thickness- dependent. Argonne National Laboratory's work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract DE-AC02-06CH11357.

3D-ΔPDF: a routine method for analyzing diffuse scattering from single crystals.

With the recent advances in x-ray area detectors, high quality diffuse scattering became readily available. This allows to investigate local order in single crystals and provides invaluable information about real structures of disordered crystals, e.g. stacking probabilities, or structural dynamics. Recently, a new method called Three Dimensional Difference Pair Distribution Function (3D-ΔPDF) analysis was introduced [1]. It provides direct access to the short range order correlations and allows to investigate the diffuse scattering of both static and dynamic origin in a unified fashion . The method is similar to the powder PDF, but availability of three dimensional diffraction data provides several key differences. Firstly, it allows elimination of Bragg peaks and refinement of diffuse scattering alone which conveniently separates the investigation of average structure from investigation of ordering. Secondly, due to reduced overlap of PDF signals, the correlation coefficients at very long interatomic vectors become accessible. The 3D-ΔPDF analysis can be performed in the newly developed program Yell [2]. The program supports all types of correlations and contains a fast FFT-based method for diffuse scattering calculation, and the constraints of arbitrary arithmetic expressions.