X-ray Transmission Measurements Research Articles

Experimental determination of the hafnium L-subshell fundamental parameters using the holistic approach

By employing the recently demonstrated new holistic approach, the atomic fundamental parameters (FPs) of the three Hf-L subshells were experimentally determined using the radiometrically calibrated instrumentation of the Physikalisch-Technische Bundesanstalt. The Coster–Kronig factors, the L-subshell fluorescence yields, the L-subshell Auger yields, the subshell-photoionization cross sections, and the subshell fluorescence production cross sections were determined by means of photon energy dependent x-ray fluorescence and transmission measurements. The recently demonstrated new holistic evaluation approach allows to determine the FPs with significantly lower uncertainties as compared to the former data evaluation scheme, where only a limited regime of incident photon energies is being probed and the data evaluation scheme is performed in a sequential manner.

Development of Lead-Free Radiation Shielding Material Utilizing Barium Sulfate and Magnesium Oxide as Fillers in Addition Cure Liquid Silicone Rubber.

The radiological protection has the purpose of safeguarding the physical well-being of the user, preventing exposure to detrimental levels of ionizing radiation. This study introduces a novel, cost-effective category of lead-free elastomeric material designed for radiation shielding. The filler compounds utilized are notably lighter than conventional lead-based materials, enhancing user ergonomics during application. They comprise of a blend of barium sulfate combined or not with magnesium oxide with addition-cure liquid silicone rubber. To ensure the effectiveness of the radiation shielding, X-ray transmission measurements were performed for the different thicknesses of the materials and the results compared with Monte Carlo simulations. Additionally, the physical properties of the new materials, such as density, homogeneity, tensile strength, viscosity, and wettability, were also evaluated. The findings indicate that both materials fulfill the requirement for application in radiation protection garments.

Super cold-crystallization of sodium iodine in selenium based chalco-halide glasses

Mechanical properties of a chalco-halide glass of the composition (0.72 GeSe2–0.28 Ga2Se3)75 NaI25 are studied during isothermal treatment below Tg (Tg-60 °C). The evolution of the Young's Modulus (E), the damping (Q−1) and the apparent viscosity (J−1, reverse of the creep rate) during heat treatment show that a structural rearrangement occurs in the glass below Tg. X-Ray diffraction and transmission measurements of the sample after heat treatment highlight the beginning of a super cold crystallization of cubic NaI within the glass after 1 month at Tg-60 °C. After 3 months of heat treatment, NaI crystals of about 31 nm size have been observed in the glass matrix by transmission electron microscopy.

Angular X-ray transmission measurements of gold absorption gratings: comparison of different laboratory X-ray sources

Over the past few years, numerous advances have been made in X-ray imaging technology. X-ray imaging plays an important role in the non-destructive exploration of the internal structures of objects for research, medical and industrial applications. When X-rays are used in computed tomography (CT), the differences in density of various components of a specimen result in different degrees of absorption of the X-rays and are ultimately responsible for image formation and image contrast. However, in some situations, this contrast is not sufficient for the sample, e.g. in the case of fossils embedded in rock, there are often situations where the fossil and rock have similar grey values. Poor contrast causes the loss of valuable detail and makes further image processing steps such as segmentation challenging. There is a continuous need to improve and develop new image acquisition techniques with the goal to improve the quality of the obtained CT data. Computed tomography techniques have been extended to phase contrast imaging in recent years using the principle of Talbot-Lau interferometers. Initially performed in synchrotron facilities the method was extended to work with incoherent polychromatic X-ray sources by introducing a source grating into the setup and therefore reducing the requirements on the spatial coherence of the source significantly. In this work, we report on the experimental characterization of gold absorption gratings used in such a laboratory-based cone-beam phase contrast setup. The gold gratings are characterized by Angular X-ray Transmission using different laboratory X-ray sources, providing insights not only into the grating feature sizes but also validating the suitability of the available laboratory source for phase contrast imaging. This work is the first step in a project implementing phase contrast X-ray imaging in laboratory setups in South Africa.

Iodine tomographic images derived from a small number of X-ray transmission measurements using material thickness distributions

ABSTRACT With the final aim of achieving iodine contrast-enhanced cancer screening examinations with low dose exposure, we reconstructed tomographic images of material distributions from X-ray transmission measurements obtained from a small number of measurement directions. This method used a planar-type four-channel ‘transXend’ detector. The phantom was subjected to four different X-ray spectra tailored by filters, and the X-rays were measured by a flat panel detector. The X-ray attenuation by the phantom was reproduced according to attenuations by acrylic, iodine, and aluminum, which acted as substitutes for normal tissue, iodine contrast agent, and bone, respectively. The material thickness distributions obtained were used for tomographic image reconstruction of the material distribution. The quality of iodine tomographic images is discussed as a function of the number of measurement directions.

High-Pressure Investigation of 2,4,6-Trinitro-3-bromoanisole (TNBA): Structural Determination and Piezochromism

Understanding phase transitions in energetic materials is crucial for developing predictive models of detonation. 2,4,6-Trinitro-3-bromoanisole (TNBA), an energetic material, was studied in its single-crystal form up to pressures of 45 GPa in a diamond anvil cell. The material was characterized by using X-ray, Raman, and optical transmission measurements. From single-crystal X-ray diffraction, the ambient structure of TNBA was determined which crystallizes in the P21/c space group having four molecular units per unit cell. The X-ray data up to 9.2 GPa were fitted to a third-order Birch–Murnaghan equation of state by using the parameters K0 = 13.2(2.4) GPa and Kp = 5.1(1.4). Between 6.8 and 7.3 GPa, a phase transition was inferred in TNBA from concurrent fading of X-ray diffraction, disappearance of Raman peaks, increase in sample fluorescence, and discontinuous color change. The new phase was consistent with an amorphous state of at least partially intact molecules judging from the presence of higher-order Raman modes and irreversibility of the Raman spectra upon release. Piezochromism was observed with the translucent yellow TNBA gradually darkening and becoming opaque black at ∼25 GPa. This correlated to the absorption edge gradually shifting to the red in the visible spectrum. Signs of two possible additional structural transitions were detected in the 32.4–41.0 GPa range as suggested by a jump in the absorption edge, the irreversible changes in the absorption spectrum upon release to ambient pressure, and by the lack of Raman modes in recovered samples. The crystal and electronic structures of TNBA were also investigated up to 10 GPa by using DFT calculations and crystal structure prediction (CSP) simulations. In agreement with the experimentally observed transition at 7 GPa, the simulations at 10 GPa found a bevy of polymorphs lower in enthalpy and higher in density than P21/c. The lowest calculated enthalpy structure was determined to be P212121, being in a different space group than the ambient experimental result.

Superior X-ray radiation shielding of biocompatible platform based on reinforced polyaniline by decorated graphene oxide with interconnected tungsten–bismuth–tin complex

Nowadays, upon rapid advances and developments in science and technology, X-ray radiation's role in diverse kinds of applications has been highlighted. Lead, and its derivatives as preliminary shielding systems are neither light nor biocompatible. Accordingly, the demand for the fabrication of a lead-free shielding system has increased over the past few decades. To surmount the limitations mentioned above, we have synthesized a novel X-ray radiation shield based on reinforced polyaniline with hybrid graphene oxide nanoflakes decorated with an interconnected complex of tungsten-bismuth-tin, which possesses high inhibitory effects against different microorganisms. Besides, diverse kinds of characterization techniques were employed to assess the as developed nanoflakes' successful fabrication. The radiation attenuation properties of developed nanomaterials and nanocomposites were explored using X-ray (i.e., 40, 60, 80, 100 and 120 keV) transmission measurements. The increasing thickness of the shield substantially developed the attenuation efficiency because thickening the samples would intensify the adequate number of the developed nanoparticles in the pathway of incident photons. The shield's thickest layer's attenuation efficiency and linear attenuation coefficient were 98.09% and 0.4399 1.mm-1, respectively, at the photon energy of 120 keV. The obtained results of the minimum inhibitory concentration (MIC) test and cell viability assay furtherly confirmed the favourable antibacterial/antifungal effects and non-toxic nature of the developed shields. According to the results, the developed shield can be effectively used to make lighter radiation protective clothes, e.g. aprons, gonad shields, thyroid shields, and structural shielding in X-ray facilities.

Xenon Plasma Focused Ion Beam Milling for Obtaining Soft X-ray Transparent Samples

We employ xenon (Xe) plasma focused ion beam (PFIB) milling to obtain soft X-ray transparent windows out of bulk samples. The use of a Xe PFIB allows for the milling of thin windows (several 100 nm thick) with areas of the order of 100 µm × 100 µm into bulk substrates. In addition, we present an approach to empirically determine the transmission level of such windows during fabrication by correlating their electron and soft X-ray transparencies. We perform scanning transmission X-ray microscopy (STXM) imaging on a sample obtained by Xe PFIB milling to demonstrate the conceptual feasibility of the technique. Our thinning approach provides a fast and simplified method for facilitating soft X-ray transmission measurements of epitaxial samples and it can be applied to a variety of different sample systems and substrates that are otherwise not accessible.

The New Paradox of Dual Modality X-Ray Diamond Sorting

Modern-day diamond sorting is achieved through the application of X-ray luminescence (XRL) and X-ray transmission (XRT) techniques. Sorting with XRL is limited to the class range of 1.25 mm to 32 mm because of self-absorption associated with larger diamonds, greater than 32mm. The effect of self-absorption is also a high-energy phenomenon in XRL. XRT is limited to sorting large size diamonds as the technique suffers poor contrast for diamonds smaller than 10mm. XRT measurements are immune to self-absorption for all sample sizes, while XRL measurements have good contrast for particles smaller than 32mm. The applications of these techniques have hitherto been used independently of each other and have subsequently progressed mutually exclusively. Here we analytically show a new paradox of a dual-modality X-ray diamond sorting combining XRL and XRT techniques' strengths. Key features of our new paradoxical model performance are contrast mitigation for small particles and self-absorption rejection for a large particle at high energy as well as improved particle detectability and classification.

Experimental study of photon-counting CT neural network material decomposition under conditions of pulse pileup.

.Purpose: We investigated the performance of a neural network (NN) material decomposition method under varying pileup conditions.Approach: Experiments were performed at tube current settings that provided count rates incident on the detector through air equal to 9%, 14%, 27%, 40%, and 54% of the maximum detector count rate. An NN was trained for each count-rate level using transmission measurements through known thicknesses of basis materials (PMMA and aluminum). The NN trained for each count-rate level was applied to x-ray transmission measurements through test materials and to CT data of a rod phantom. Material decomposition error was evaluated as the distance in basis material space between the estimated thicknesses and ground truth.Results: There was no clear trend between count-rate level and material decomposition error for all test materials except neoprene. As an example result, Teflon error was 0.33 cm at the 9% count-rate level and 0.12 cm at the 54% count-rate level for the x-ray transmission experiments. Decomposition error increased with count-rate level for the neoprene test case, with 0.65-cm error at 9% count-rate level and 1.14-cm error at the 54% count-rate level. In the CT study, material decomposition error decreased with increasing incident count rate. For example, the material decomposition error for Teflon was 0.089, 0.066, 0.054 at count-rate levels of 14%, 27%, and 40%, respectively.Conclusions: Results demonstrate over a range of incident count-rate levels that an NN trained at a specific count-rate level can learn the relationship between photon-counting spectral measurements and basis material thicknesses.

Experimental observations of exploding bridgewire detonator function

Exploding bridgewire detonators are an industry standard technology used for over 75 years and valued for their precise timing and safety characteristics. Despite widespread use, their functional mechanism remains controversial with both shock and non-shock mechanisms attributed. In this work, we reexamine the bridgewire detonator function with a suite of modern diagnostics and compare these observations with the existing literature. Traditional detonator observations consisted of voltage applied to the bridgewire and time dependent current, integral response measurements such as case motion, and more recently Schlieren imaging of the detonator surface. In this work, we add visible light emission, x-ray transmission, proton radiography, and temperature measurements during detonator function in addition to voltage, current, and function times. The addition of in situ observations of light emission, temperature, and density gives us new insight into the mechanisms of explosive bridgewire detonator function. We see a distinct separation in time, location, symmetry, and velocity of bridgewire output and detonation onset. During the time between bridgewire burst and the initiation of detonation, we observe a temperature ramp in the input pellet. In this paper, we present the suite of measurements and comparisons with the literature on integral response measurements.

Preparation of PVC/Bi2O3 composites and their evaluation as low energy X-Ray radiation shielding

Plasticized and gamma crosslinked PVC composites were prepared by adding different amounts of Bi2O3 particles to evaluate their low energy X-ray radiation shielding properties. Composites were gamma-irradiated in an industrial irradiator (60Co source) at the corresponding times to obtain a dose of 75 kGy to enhance mechanical properties through crosslinking. The shielding properties of composites were obtained by X-ray transmission measurements at low energies (X-ray tube voltages range 20–61 kV) by using a mammography unit and an X-ray hospital equipment. A small influence in the dehydroclorination reaction of PVC was observed during decomposition in TGA experiments due to Bi2O3 nanoparticle content, but DMA results show improved viscoelastic properties for the crosslinked composites. The X-ray transmission values decrease as a function of nanoparticle content, observing an increase in the transmission values (low attenuation) at higher energies. The composite with 50 %wt of Bi2O3 showed the lowest transmission values, at X-ray tube voltages 20–30 kV, the transmittance was almost nil, and then it increases ~27% at 61 kV.

Synchrotron x-ray transmission measurements and modeling of filters investigated for Athena

Advanced Telescope for High-Energy Astrophysics is a large-class astrophysics space mission selected by the European Space Agency to study the theme “Hot and Energetic Universe.” The mission essentially consists of a large effective area x-ray telescope and two detectors: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager (WFI). Both instruments require filters to shield from out-of-band radiation while providing high transparency to x-rays. The mission is presently in phase B; thus, to consolidate the preliminary design, investigated filter materials need to be properly characterized by experimental test campaigns. We report results from high-resolution x-ray transmission measurements performed using different synchrotron radiation beamlines to assess the filter calibration accuracy and mitigate the risk related to selecting a unique calibration facility. The main goals of these test campaigns are (i) to verify the compliance of the investigated filter design to the scientific requirements, (ii) to develop an accurate x-ray transmission model, and (iii) to start identifying suitable measurement facilities and achievable accuracy for the flight filters calibration program. In particular, the x-ray transmission model of the X-IFU and WFI filters has been refined within the edges of Al, C, N, and O by deriving the optical constants from two reference samples measured by synchrotron light. The achievable filter calibration accuracy has been estimated by evaluating the agreement between the best-fit according to the developed transmission model and the experimental data.

Soft X-ray absorption of thin films detected using substrate luminescence: a performance analysis.

X-ray absorption spectroscopy of thin films is central to a broad range of scientific fields, and is typically detected using indirect techniques. X-ray excited optical luminescence (XEOL) from the sample's substrate is one such detection method, in which the luminescence signal acts as an effective transmission measurement through the film. This detection method has several advantages that make it versatile compared with others, in particular for insulating samples or when a probing depth larger than 10 nm is required. In this work a systematic performance analysis of this method is presented with the aim of providing guidelines for its advantages and pitfalls, enabling a wider use of this method by the thin film community. The efficiency of XEOL is compared and quantified from a range of commonly used substrates. These measurements demonstrate the equivalence between XEOL and X-ray transmission measurements for thin films. Moreover, the applicability of XEOL to magnetic studies is shown by employing XMCD sum rules with XEOL-generated data. Lastly, it is demonstrated that above a certain thickness XEOL shows a saturation-like effect, which can be modelled and corrected for.

Quality and parameter control of X-ray absorption gratings by angular X-ray transmission.

Here we report on a non-destructive, spatially resolving and easy to implement quality and parameter control method for high aspect ratio X-ray absorption gratings. Based on angular X-ray transmission measurements, our proposed technique allows to determine the duty cycle, the transmittance, the height, as well as the local inclination of the absorbing grating structures. A key advantage of the presented method is a fast and extensive grating quality evaluation without the need of implementing an entire grating interferometer. In addition to the local and surface-based analysis using a scanning electron microscope, our non-destructive method provides global averaged macroscopic and spatially resolved grating structure information without the requirement of resolving individual grating lines.

Salt concentration and charging velocity determine ion charge storage mechanism in nanoporous supercapacitors

A fundamental understanding of ion charge storage in nanoporous electrodes is essential to improve the performance of supercapacitors or devices for capacitive desalination. Here, we employ in situ X-ray transmission measurements on activated carbon supercapacitors to study ion concentration changes during electrochemical operation. Whereas counter-ion adsorption was found to dominate at small electrolyte salt concentrations and slow cycling speed, ion replacement prevails for high molar concentrations and/or fast cycling. Chronoamperometry measurements reveal two distinct time regimes of ion concentration changes. In the first regime the supercapacitor is charged, and counter- and co-ion concentration changes align with ion replacement and partially co-ion expulsion. In the second regime, the electrode charge remains constant, but the total ion concentration increases. We conclude that the initial fast charge neutralization in nanoporous supercapacitor electrodes leads to a non-equilibrium ion configuration. The subsequent, charge-neutral equilibration slowly increases the total ion concentration towards counter-ion adsorption.

In situ X-ray monitoring of transport and chemistry of Ga-containing intermediates under ammonothermal growth conditions of GaN

Formation and transport of Ga-containing intermediates are essential for ammonothermal bulk growth of GaN. In this work, in situ X-ray transmission measurements are established as a tool for monitoring face-selective dissolution of GaN crystals as well as the Ga-concentration in the fluid. The accuracy of concentration determination by X-ray transmission measurements is evaluated and the detection limit for dissolved species is estimated. The detection limit is given both as a gallium concentration and as an attenuation coefficient, thus, it can easily be transferred to other materials of interest. Face-selective ammonothermal etching is investigated for both ammonoacidic and ammonobasic mineralizers. Time- and space-resolved monitoring of the concentration of Ga-containing intermediates is demonstrated using NH4F mineralizer. The results are discussed with respect to the formation of Ga-containing intermediates and mechanisms of mass transport. Based on molecular dynamics simulations, the experimentally observed, unexpectedly low diffusion coefficient for the Ga-transporting species is ascribed at least partially to the diffusion of larger [GaxFy]3x−y aggregates.

Update 2017 on Target Fabrication Requirements for High-Performance NIF Implosion Experiments

Experiments and analysis in the 2 years since the 2015 Target Fabrication Meeting have resulted in further evolution of the requirements for high-performance layered implosions. This paper is a status update on the experimental program and supporting modeling, with emphasis on the implications for fabrication requirements. Previous work on the capsule support has continued, with various other support options being explored in experiments and modeling. Work also continues on ablator composition nonuniformities, with important new results from CH experiments on Omega, and the first three-dimensional X-ray transmission measurements of Be capsules on the National Ignition Facility. Work on hohlraums continues to include near-vacuum hohlraums and U hohlraums without a gold lining. Overall, the understanding that has been achieved, along with the progress in fabrication technology, represents good continuing progress toward the goal of fusion in the laboratory.

Modeling Non-Equilibrium Dynamics and Saturable Absorption Induced by Free Electron Laser Radiation

Currently available X-ray and extreme ultraviolet free electron laser (FEL) sources provide intense ultrashort photon pulses. Those sources open new exciting perspectives for experimental studies of ultrafast non-equilibrium processes at the nanoscale in condensed matter. Theoretical approaches and computer simulations are being developed to understand the complicated dynamical processes associated with the interaction of FEL pulses with matter. In this work, we present the results of the application of a simplified three-channel model to the non-equilibrium dynamics of ultrathin aluminum films excited by FEL radiation at 33.3, 37 and 92 eV photon energy. The model includes semi-classical rate equations coupled with the equation of propagation of the photon wave packets. X-ray transmission measurements are found to be in agreement with present simulations, which are also able to shed light on temporal dynamics (in the fs range) in nano-sized Al films strongly interacting with the photon pulse. We also expanded our non-linear model, explicitly including the two-photon absorption cross-section and the effect of including electron heating for reproducing transmission measurements.

Numerical investigations of potential systematic uncertainties in iron opacity measurements at solar interior temperatures.

Iron opacity calculations presently disagree with measurements at an electron temperature of ∼180-195 eV and an electron density of (2-4)×10^{22}cm^{-3}, conditions similar to those at the base of the solar convection zone. The measurements use x rays to volumetrically heat a thin iron sample that is tamped with low-Z materials. The opacity is inferred from spectrally resolved x-ray transmission measurements. Plasma self-emission, tamper attenuation, and temporal and spatial gradients can all potentially cause systematic errors in the measured opacity spectra. In this article we quantitatively evaluate these potential errors with numerical investigations. The analysis exploits computer simulations that were previously found to reproduce the experimentally measured plasma conditions. The simulations, combined with a spectral synthesis model, enable evaluations of individual and combined potential errors in order to estimate their potential effects on the opacity measurement. The results show that the errors considered here do not account for the previously observed model-data discrepancies.