Broad X-ray Spectrum Research Articles

Evidence for a Cyclotron Absorption Line and Spectral Transition in EXO 2030+375 during the 2021 Giant Outburst

Based on Insight-HXMT observations of EXO 2030+375 during its 2021 giant outburst, we report the analysis of pulse variations and the broadband X-ray spectrum, and find the presence of a potential cyclotron resonant scattering feature (CRSF) with the fundamental line at ∼47 keV from both average spectra and phase-resolved spectroscopy. During the outburst, the source reached an X-ray luminosity of ∼1038 erg s−1 from 2 to 105 keV at a distance of 7.1 kpc. The X-ray pulsar at the spin period of 41.27 ± 0.61 s exhibits complex timing and spectral variations with both energy and luminosity during the outburst. The shapes of the pulse profiles show the single main peak above ∼20 keV, while appearing to exhibit multipeak patterns in low-energy bands, and the transition of the 10–20 keV pulse profiles from multipeak to single peak is observed at ∼0.8 × 1038 erg s−1, which suggests the evolution from the subcritical luminosity (pencil-beam dominated) to the supercritical luminosity (fan-beam dominated) regime. A dip structure before the energy of the CRSFs is found in the pulse fraction–energy relation of EXO 2030+375 near the peak luminosity. A detailed analysis of spectral parameters showed that the power-law photon index exhibits three distinct trends as luminosity increases, and these spectral changes also signify a spectral transition from subcritical to supercritical regimes. The critical luminosity infers a magnetic field of ∼(4.8−6.0) × 1012 G, which supports the presence of the cyclotron line at ∼47 keV. A Comptonization model applied for the broad X-ray spectra during the outburst also suggests the surface magnetic field ranging from ∼(5−9) × 1012 G.

Printable Perovskite Diodes for Broad-Spectrum Multienergy X-Ray Detection.

Multienergy X-ray detection is critical to effectively differentiate materials in a variety of diagnostic radiology and nondestructive testing applications. Silicon and selenium X-ray detectors are the most common for multienergy detection; however, these present poor energy discrimination across the broad X-ray spectrum and exhibit limited spatial resolution due to the high thicknesses required for radiation attenuation. Here, an X-ray detector based on solution-processed thin-film metal halide perovskite that overcomes these challenges is introduced. By harnessing an optimized n-i-p diode configuration, operation is achieved across a broad range of soft and hard X-ray energies stemming from 0.1 to 10's of keV. Through detailed experimental and simulation work, it is shown that optimized Cs0.1 FA0.9 PbI3 perovskites effectively attenuate soft and hard X-rays, while also possessing excellent electrical properties to result in X-ray detectors with high sensitivity factors that exceed 5 × 103 and 6 × 104 µC Gy-1 cm-2 within soft and hard X-ray regimes, respectively. Harnessing the solution-processable nature of the perovskites, roll-to-roll printable X-ray detectors on flexible substrates are also demonstrated.

Alanine response to low energy synchrotron x-ray radiation

Objective. The radiation response of alanine is very well characterized in the MV photon energy range where it can be used to determine the dose delivered with an accuracy better than 1%, making it suitable as a secondary standard detector in cancer radiation therapy. This is not the case in the very low energy keV x-ray range where the alanine response is affected by large uncertainties and is strongly dependent on the x-ray beam energy. This motivated the study undertaken here. Approach. Alanine pellets with a nominal thickness of 0.5 mm and diameter of 5 mm were irradiated with monoenergetic x-rays at the Diamond Light Source synchrotron, to quantify their response in the 8–20 keV range relative to 60Co radiation. The absorbed dose to graphite was measured with a small portable graphite calorimeter, and the DOSRZnrc code in the EGSnrc Monte Carlo package was used to calculate conversion factors between the measured dose to graphite and the absorbed dose to water delivered to the alanine pellets. GafChromic EBT3 films were used to measure the beam profile for modelling in the MC simulations. Main results. The relative responses measured in this energy range were found to range from 0.616 to 0.643, with a combined relative expanded uncertainty of 3.4%–3.5% (k = 2), where the majority of the uncertainty originated from the uncertainty in the alanine readout, due to the small size of the pellets used. Significance. The measured values were in good agreement with previously published data in the overlapping region of x-ray energies, while this work extended the dataset to lower energies. By measuring the response to monoenergetic x-rays, the response to a more complex broad-spectrum x-ray source can be inferred if the spectrum is known, meaning that this work supports the establishment of alanine as a secondary standard dosimeter for low-energy x-ray sources.

Dual-Energy X-ray Medical Imaging with Inverse Compton Sources: A Simulation Study

It has been long recognized that dual-energy imaging could help to enhance the detectability of lesions in diagnostic radiology, by removing the contrast of surrounding tissues. Furthermore, X-ray attenuation is material specific and information about the object constituents can be extracted for tissue characterisation, i.e., to assess whether lesions represent a malignant or benign process. However, a true separation between the low and high energy components is not possible with conventional sources because of their broad X-ray spectrum, and the artifacts produced in the subtracted image can be only partially removed. Finally, dose issues have also prevented so far the application of dual-energy techniques within the clinical context. Very recently, a new intense and monochromatic X-ray source was proposed to fill the gap between a synchrotron radiation facility and the standard X-ray tube. Indeed, inverse Compton scattering (ICS) sources, which are based on the interaction of a powerful laser beam and a bright beam of relativistic electrons, are among the most promising innovative sources of monochromatic X and gamma radiation. In this contribution, we review the main features that allow an ICS source to meet the requirements of a medical imaging application. Specific examples of K-edge subtraction are then provided, to show the potential of ICS in clinical applications that require intravenous injection of a contrast medium.

Optimization procedure for a Talbot-Lau x-ray phase-contrast imaging system

In Talbot-Lau x-ray imaging, the fringe visibility provided by the interferometer is a crucial quality parameter to preserve high quality images at an acceptable dose level. The noise of the obtained differential phase signal and the dark-field image is directly influenced by the visibility. To optimize the performance of such an interferometer, we use wave-field simulations to investigate the effect of the phase grating G1. Therefore, we varied the grating parameters duty cycle and grating bar height. Each set of these parameters were evaluated for different propagation distances and for multiple x-ray spectra. In this multidimensional space the interferometer configuration with the highest visibility over a wide range of energies was selected to cover a multiple possible x-ray applications. We manufactured the optimized phase grating G1, the corresponding source grating G0 and analyzer grating G2 and compare the experimental results with the expected results obtained from simulations. The presented measurements show outstanding visibilities up to 50% using a broad x-ray spectrum. These measurements are in very good agreement to the simulation results. The achieved visibility is up to two times higher than for a standard-type setup. This enhancement results in high quality images at a reasonable dose level which we exemplarily demonstrate by imaging a foreign object in a pork trotter.

MultiLaue: A Technique to Extract d-spacings from Laue XRD

doi:10.1017/S1431927616009764 Microsc. Microanal. 22 (Suppl 3), 2016 © Microscopy Society of America 2016 MultiLaue: A Technique to Extract d-spacings from Laue XRD Zack Gainsforth 1 , Matthew A. Marcus 2 , Nobumichi Tamura 2 and Andrew J. Westphal 1 University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, 91020, USA Lawrence Berkeley Laboratory, Advanced Light Source, Berkeley, CA, 91020, USA Broad spectrum X-ray Diffraction (XRD) is named Laue after Max von Laue, and is the original XRD technique [1]. Today, monochromatic XRD is more common because Bragg's equation allows determination of d-spacings where Laue does not. Laue still remains in use for single crystal systems because it can be used to make very accurate unit cell determinations as well as for strain and orientation mapping. A Laue technique which could provide unambiguous determination of lattice spacings, a la Bragg's equation would be a huge leap forward, especially for multiphase samples such as meteorites, interplanetary dust particles and some geological specimens. We introduce a new technique we call multiLaue which allows such determination. First an unfiltered Laue pattern is acquired. Then a filter is inserted between the radiation source and the sample – in this case a 100 um thick fused silica wafer – and a new Laue pattern is acquired. A shield protects the detector from radiation scattered off the filter. Low energy X-rays are more strongly absorbed by the filter than high energy X-rays so reflections excited by low energies are more attenuated relative to those excited by high energies. We developed a computer model simulating the process, and use it to quantitatively determine the X-ray energy exciting a reflection based on the reduction of intensity across a set of three filters (100, 200 and 300 micron fused silica). We tested multiLaue on a Si chip on beamline 12.3.2 at the Advanced Light Source synchrotron. The unfiltered pattern is shown in Figure 1. We analyzed 32 reflections (Table 1) and computed best fit energies. These are compared with energies based on indexation via the XMAS software [2]. The best fit energies matched well between 11 and 23 keV, with a mean relative error of 1.9% and a standard deviation of the error of 1.4%. This means we can compute d-spacings with an accuracy of 21 keV have large errors. Reflections < 11 keV have a harmonic contribution from the spectrum above 21 keV and also show large errors. Therefore, accurate characterization of the radiation source, and optics is crucially important to achieving high accuracy quantification.

Photon counting x-ray imaging with K-edge filtered x-rays: A simulation study.

In photon counting (PC) x-ray imaging and computed tomography (CT), the broad x-ray spectrum can be split into two parts using an x-ray filter with appropriate K-edge energy, which can improve material decomposition. Recent experimental study has demonstrated substantial improvement in material decomposition with PC CT when K-edge filtered x-rays were used. The purpose of the current work was to conduct further investigations of the K-edge filtration method using comprehensive simulation studies. The study was performed in the following aspects: (1) optimization of the K-edge filter for a particular imaging configuration, (2) effects of the K-edge filter parameters on material decomposition, (3) trade-off between the energy bin separation, tube load, and beam quality with K-edge filter, (4) image quality of general (unsubtracted) images when a K-edge filter is used to improve dual energy (DE) subtracted images, and (5) improvements with K-edge filtered x-rays when PC detector has limited energy resolution. The PC x-ray images of soft tissue phantoms with 15 and 30 cm thicknesses including iodine, CaCO3, and soft tissue contrast materials, were simulated. The signal to noise ratio (SNR) of the contrast elements was determined in general and material-decomposed images using K-edge filters with different atomic numbers and thicknesses. The effect of the filter atomic number and filter thickness on energy separation factor and SNR was determined. The boundary conditions for the tube load and halfvalue layer were determined when the K-edge filters are used. The material-decomposed images were also simulated using PC detector with limited energy resolution, and improvements with K-edge filtered x-rays were quantified. The K-edge filters with atomic numbers from 56 to 71 and K-edge energies 37.4-63.4 keV, respectively, can be used for tube voltages from 60 to 150 kVp, respectively. For a particular tube voltage of 120 kVp, the Gd and Ho were the optimal filter materials to achieve highest SNR. For a particular K-edge filter of Gd and tube voltage of 120 kVp, the filter thickness 0.6 mm provided maximum SNR for considered imaging applications. While K-edge filtration improved SNR of CaCO3 and iodine by 41% and 36%, respectively, in DE subtracted images, it did not deteriorate SNR in general images. For x-ray imaging with nonideal PC detector, the positive effect of the K-edge filter was increased when FWHM energy resolution was degraded, and maximum improvement was at 60% FWHM. This study has shown that K-edge filtered x-rays can provide substantial improvements of material selective PC x-ray and CT imaging for nearly all imaging applications using 60-150 kVp tube voltages. Potential limitations such as tube load, beam hardening, and availability of filter material were shown to not be critical.

Do Textiles Impact DXA Bone Density/Body Composition Results?

Osteoporotic patients treated with strontium ranelate show relatively large increases in bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) due to the replacement of some of the calcium atoms in bone by strontium. A study published by Pors Nielsen and colleagues reported that replacement of 1% of calcium atoms by strontium causes a 10% increase in BMD. We refer to the ratio of the percentage increase in BMD to the molar percentage of strontium in bone as the strontium ratio. Theoretically it is expected that the strontium ratio should vary between different manufacturers' DXA equipment depending on the effective photon energy of the device, an effect that arises because of the proximity of the X-ray energies produced by lower energy devices to the strontium K-edge at 16 keV. In this study we report theoretical estimates of the strontium ratio for two axial DXA systems and two peripheral DXA devices based on their broad spectrum X-ray emission. The theoretical figures were verified in an experimental study in which the strontium ratio for each device was measured using phantoms containing mixtures of hydroxyapatite and strontium hydrogen-phosphate. The theoretical values of the strontium ratio were 11.0 for the Hologic Discovery, 9.9 for the GE-Lunar Prodigy, 9.1 for the Demetech Calscan, and 8.5 for the Osteometer Dexacare G4. Experimental results were 11.2 for the Discovery, 9.9 for the Prodigy, 8.6 for the Calscan and 6.3 for the Dexacare G4. The results confirm both theoretically and experimentally that the effect of bone strontium on BMD measurements is different for different DXA systems. In the future it might be possible to exploit this effect to make a non-invasive estimate of average bone strontium content in groups of patients receiving strontium medication for osteoporosis.

Energy Calibration of a Silicon-Strip Detector for Photon-Counting Spectral CT by Direct Usage of the X-ray Tube Spectrum

The variation among energy thresholds in a multibin detector for photon-counting spectral CT can lead to ring artefacts in the reconstructed images. Calibration of the energy thresholds can be used to achieve homogeneous threshold settings or to develop compensation methods to reduce the artefacts. We have developed an energy-calibration method for the different comparator thresholds employed in a photon-counting silicon-strip detector. In our case, this corresponds to specifying the linear relation between the threshold positions in units of mV and the actual deposited photon energies in units of keV. This relation is determined by gain and offset values that differ for different detector channels due to variations in the manufacturing process. Typically, the calibration is accomplished by correlating the peak positions of obtained pulse-height spectra to known photon energies, e.g. with the aid of mono-energetic x rays from synchrotron radiation, radioactive isotopes or fluorescence materials. Instead of mono-energetic x rays, the calibration method presented in this paper makes use of a broad x-ray spectrum provided by commercial x-ray tubes. Gain and offset as the calibration parameters are obtained by a regression analysis that adjusts a simulated spectrum of deposited energies to a measured pulse-height spectrum. Besides the basic photon interactions such as Rayleigh scattering, Compton scattering and photo-electric absorption, the simulation takes into account the effect of pulse pileup, charge sharing and the electronic noise of the detector channels. We verify the method for different detector channels with the aid of a table-top setup, where we find the uncertainty of the keV-value of a calibrated threshold to be between 0.1 and 0.2 keV.

Fast X-ray microdiffraction techniques for studying irreversible transformations in materials

A pair of techniques have been developed for performing time-resolved X-ray microdiffraction on irreversible phase transformations. In one technique capillary optics are used to focus a high-flux broad-spectrum X-ray beam to a 60 µm spot size and a fast pixel array detector is used to achieve temporal resolution of 55 µs. In the second technique the X-rays are focused with Kirkpatrick-Baez mirrors to achieve a spatial resolution better than 10 µm and a fast shutter is used to provide temporal resolution better than 20 µs while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils.

Requirements for commercial X-ray element-specifc imaging technology

Analysis of the composition of material samples non-destructively by means of standard X-ray tube imaging is extremely challenging due to the breadth of the bremsstrahlung spectrum, resulting from mono-energetic electrons striking a thick tungsten target. In previous work, stacks of registered field-flattened images of various samples over an energy range 15-150 keVwere created and analysed. Attempts to remove the effects of the broad spectrum proved the concept of element-specific imaging, but problems still remained. In this work, modification strategies to existing designs are proposed in both hardware and software, which would bolster efforts to remove the effects of the broad X-ray spectrum.

The effect of bone strontium on BMD is different for different manufacturers' DXA Systems

Osteoporotic patients treated with strontium ranelate show relatively large increases in bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) due to the replacement of some of the calcium atoms in bone by strontium. A study published by Pors Nielsen and colleagues reported that replacement of 1% of calcium atoms by strontium causes a 10% increase in BMD. We refer to the ratio of the percentage increase in BMD to the molar percentage of strontium in bone as the strontium ratio. Theoretically it is expected that the strontium ratio should vary between different manufacturers' DXA equipment depending on the effective photon energy of the device, an effect that arises because of the proximity of the X-ray energies produced by lower energy devices to the strontium K-edge at 16 keV. In this study we report theoretical estimates of the strontium ratio for two axial DXA systems and two peripheral DXA devices based on their broad spectrum X-ray emission. The theoretical figures were verified in an experimental study in which the strontium ratio for each device was measured using phantoms containing mixtures of hydroxyapatite and strontium hydrogen-phosphate. The theoretical values of the strontium ratio were 11.0 for the Hologic Discovery, 9.9 for the GE-Lunar Prodigy, 9.1 for the Demetech Calscan, and 8.5 for the Osteometer Dexacare G4. Experimental results were 11.2 for the Discovery, 9.9 for the Prodigy, 8.6 for the Calscan and 6.3 for the Dexacare G4. The results confirm both theoretically and experimentally that the effect of bone strontium on BMD measurements is different for different DXA systems. In the future it might be possible to exploit this effect to make a non-invasive estimate of average bone strontium content in groups of patients receiving strontium medication for osteoporosis.

Edge-enhanced imaging obtained with very broad energy band x-rays

We demonstrate both theoretically and experimentally that edge-enhancement effects are produced when objects, in contact with the x-ray detector, are imaged by using very broad x-ray spectra. Radiographs of thin Al objects have been obtained with a table-top synchrotron source which generates x-rays in the energy range from a few kilo-electron-volts up to 6 MeV. Edge-enhancement effects arise from the combination of x-ray absorption (kilo-electron-volt part of the spectrum) and secondary particle emission (mega-electron-volt part of the spectrum) within the sample. The exact contribution of absorption and emission profiles in the edge-enhanced images has been calculated via Monte Carlo simulation.

Comparison method to differentiate between painted objects using polychromatic X-rays

X-radiography using the bremsstrahlung of a commercial broad spectrum X-ray source was used to quantify the differences and relationships between complex samples of unknown composition. The samples examined were painted and glazed ceramic mugs. The resulting pseudo-signatures were grey-level transmission spectra which can be usefully compared over a range of acceleration potential settings from 40 to 95 kV, taken at 1 kV intervals. These data are extracted from stacks of registered field-flattened X-ray images. It is shown that it is possible to differentiate between transmission spectra of the samples by concentrating mainly on the paint layers.

K-edge subtraction using an energy-resolving position-sensitive detector

Digital Subtraction Angiography is an important technique used to image arterial blood flow using an introduced contrast agent. K-edge subtraction uses contrast-agents with a K-edge feature to acquire the same information but requires knowledge of the X-ray energy and so is usually conducted using synchrotron radiation. However, given a detector that measures position and energy – rather than the currently used integrating devices – it is possible to use white-beam radiation to conduct dynamic K-edge subtraction studies. This study demonstrates an approach to this imaging possibility using analysis of the spectral histogram in each image pixel. K-edge subtraction can be conducted more efficiently using a broad-spectrum X-ray source by processing groups of data either side of the K-edge. Using a simulated data model the possible quality of this new technique is explored under a number of assumed spectral resolutions. The effects on the final image of different methods of image subtraction and pre-processing are also explored.

Using polychromatic X-radiography to examine realistic imitation firearms

Sections 36–41 of the Violent Crimes Reduction Act (2006), which came into force in England and Wales on 1st October 2007, have placed significant restrictions on the sale and possession of ‘realistic imitation firearms’. This legislation attempts to produce a definition of a ‘realistic imitation’ which clearly differentiates these items from other imitation firearms (which are not covered by the legislation). This paper will go a stage further by demonstrating techniques by which blank firing realistic imitation firearms which may be suitable for illegal conversion to fire live rounds may be differentiated from other less ‘suitable’ (but visually identical) realistic imitations. The article reports on the use of X-radiography, utilizing the bremsstrahlung of a commercial broad spectrum X-ray source, to identify the differences between alloys constituting the barrels of distinct replica and/or blank firing handguns. The resulting pseudo-signatures are transmission spectra over a range from 20 to 75 kV, taken at 1 kV intervals, which are extracted from stacks of registered, field flattened images. It is shown that it is possible to quantify differences between transmission spectra for components of different realistic imitation fire arms, and apply the results to determine the suitability of particular gun barrels from blank firing imitation firearms for illegal conversion to fire live rounds, or related illegal modifications.

Extension of x‐ray imaging linear systems analysis to detectors with energy discrimination capability

A figure of merit, the broad-spectrum generalized detective quantum efficiency, which describes the performance of digital detectors designed for broad-spectrum x-ray imaging is derived from linear response theory. This measure of the imaging efficacy of an x-ray sensor is obtained when detector contrast modulation in the domain of x-ray energy is introduced in the Fourier-based analysis of digital systems. A method is proposed to scale existing figures of merit according to the energy-dependent response of the detector and the spectral shape of the x-ray beam. The new figure of merit obtained with this method provides an extended description of system performance when comparing energy-integrating, single-photon counting, and future energy-sensitive x-ray imaging sensors. The applicability of this linear system analysis is restricted to the tasks of low-contrast object detection in radiography. The method for scaling the figure of merit to take into consideration broad-spectrum conditions is applied to mammography for future energy-dependent detectors. An approximation valid in the typical mammographic x-ray energy range is used to calculate the broad-spectrum generalized detective quantum efficiency at zero spatial frequency, for several mammographic x-ray spectra. X-ray energy weighting in mammography is investigated in the context of simulated tumors and microcalcifications detection by comparing this figure of merit, calculated for different detector technologies, under ideal imaging conditions, at zero spatial frequency.

White X-ray pulse emission of alkali halide aqueous solutions irradiated by focused femtosecond laser pulses: a spectroscopic study on electron temperatures as functions of laser intensity, solute concentration, and solute atomic number

Aqueous solutions of alkali halides were irradiated with focused femtosecond laser pulses (130 fs, 780 nm, 1 kHz) in air, and X-ray emission spectra were measured. The laser power density at the focus was estimated to be 2 PW/cm2 when the laser intensity was 0.65 mJ/pulse. Broad X-ray emission spectra having tails to the higher energy were commonly observed, often accompanied by characteristic K and L lines of solutes. Electron temperatures (Te) were obtained from the slopes of the broad X-ray spectra on the basis of the assumption of Maxwell–Boltzmann distribution of electron energy. The value of Te was 1.90 keV in the case of distilled water irradiated with laser pulses of 0.53 mJ/pulse laser pulses, while two components of Te (2.67 and 9.83 keV) were observed in the case of saturated cesium chloride aqueous solution (6.5 mol/dm3). These two components may be related to different electron acceleration processes such as inverse-bremsstrahlung and resonance absorption.

A VLSI chip set for digital radiology with energy selection

We present a compact acquisition system for digital radiology, based on GaAs detectors. The system is based on a custom VLSI circuit set, with analog and digital functions for the acquisition of radiological images in a wide range of applications. The circuit architectures and the operating principles are presented. We use a broad spectrum X-ray tube and try to exploit the full physical information contained in the incident radiation by means of both single photon counting and energy measurement of each photon.

Chemical Pulping of Straws (IV)

Among the countries using nonwood plant fiber as pulp raw materials, China is a leading country to use straw, reed, bamboo and so on (76.1% on total pulp ca. 10 million tons in 1992). However, the use of rice straw is quite small, because of a large amounts of ash, especially silica. Silica causes the scale trouble during the concentration of soda black liquor. Therefore, in order to use more rice straw for pulp production, silica trouble must be solved as soon as possible. On this point, it is also important to find the pulping method leaving silica in pulp.This paper presents the results of studies on the ash properties of straw and the behavior of rice straw ash in black liquor. The results are summarized as follows:(1) Crystalline structure of straw silica is the mixture of crystoballite and quartz type. It is interesting that the generated silica from sodium silicate in black liquor shows a diffuse, broad X-ray spectrum.(2) The ash in black liquor is removed by the addition of precipitant, namely CaO or CaO+CaCl2. The efficiency of CaCl2 addition is observed at the lower amounts of CaO addition (200% on silica) and shorter precipitation time (60 min. at 80°C). The efficiency of CaCl2 addition is not observed at higher CaO addition (300% on silica). The amounts of CaO precipitant and precipitation time can be decreased by the concentration of black liquor.(3) In order to remove separately ash and lignin in black liquor, two stage pH adjustments of black liquor are efficient.