High-resolution X-ray Radiography Research Articles

Paul Delvaux: The Study of Nine Paintings by Non-Invasive Methods

Paul Delvaux (1897–1994) was a Belgian Surrealist painter known for his dreamlike and enigmatic compositions. His works often featured nude or semi-nude women and deserted urban landscapes, evoking a sense of mystery and intrigue. Delvaux’s meticulous attention to detail and masterful use of light and shadow added depth and realism to his surrealistic style, making him one of the leading figures of the Belgian Surrealist movement. Although writings about Paul Delvaux’s work are not lacking, the literature mainly deals with the stylistic and iconographic aspects of his work. Taking an interest in painting materials and the painter’s technique allows us to understand his personality and to apprehend his work in a different way. In order to collect such information, the early painted production of Delvaux was studied in situ with imaging methods (high-resolution photography, infrared reflectography and X-ray radiography) and non-invasive analytical techniques (MA-XRF and Raman spectroscopy). The results obtained for nine oil paintings produced from 1928 to 1958 are discussed in terms of the support, the preparatory layer, the preparatory drawing, the changes in composition and reuse of paintings, the pictorial layer and the dripping phenomenon.

Investigation of key parameters for the operation of a sodium heat pipe with visualization using X-ray radiography

Alkali metal heat pipes are considered as a promising primary cooling system of special-purpose nuclear reactors. For the deployment, it is important to understand the heat pipe’s behaviors under different operation conditions. In this paper, the startup characteristics and operation performance of three sodium heat pipes with 67%, 102% and 172% sodium filling ratios, respectively, were investigated, and the two-phase sodium flow was visualized using high-speed, high-resolution x-ray radiography. The boiling flow regimes in the evaporator region were categorized into stagnant sodium liquid pool, geyser boiling and developed boiling. The effect of key parameters, such as the boundary conditions of the evaporator and condenser, the sodium filling ratio, and the inclination angle were investigated. It was found that the heater power and condenser cooling conditions have a great influence on the operation temperature within the achievable range of heat transfer rate. The filling ratio and inclination angle affect the boiling phenomena and the heat pipe operational range. The experiments can provide valuable data for heat pipe model validation as well as the design of the special-purpose nuclear reactor and other high-temperature heat pipe systems.

Fourier analysis of multi-scale neural networks implemented for high-resolution X-ray radiography

To realize high-resolution X-ray imaging, this study trains deep neural networks comprising multi-scale encoder/decoder architectures with actual data measured using a low-resolution imaging detector. The network performance is evaluated in the Fourier domain through measurements of the modulation-transfer function (MTF) and noise-power spectrum (NPS), which decompose the contrast and noise power (or variance) in terms of the spatial-frequency components. The designed networks are found to successfully deblur blurry images. The MTF analysis reflects the conventional mean-squared errors and structural similarities within it. Moreover, it indicates the over-regression property of the networks that could not be addressed via the conventional metrics. The NPS analysis reveals that the networks suppressed high-frequency noise. The Fourier analysis shows that the designed networks attempted to match the fidelity between the input and label, while suppressing noise.

Experimental Time-Lapse Visualization of Mud-Filtrate Invasion and Mudcake Deposition Using X-Ray Radiography

Accurate description and modeling of multiphase fluid flow are of paramount importance for subsurface resource engineering. The main source of information to quantify in-situ rock properties are borehole geophysical measurements, which are very often riddled with uncertainty ensuing from rock heterogeneity/anisotropy and mud-filtrate invasion effects. Therefore, experimental methods are needed to accurately describe and quantify the physics of mud-filtrate invasion and mudcake deposition and its effects on borehole geophysical measurements. We developed a new high-resolution (10 to 50 μm) experimental method to investigate the invasion of water- and oil-based drilling muds into rectangular rock samples using X-ray radiography. During mud injection, rock simples are scanned using high-resolution X-ray radiography, enabling the time-lapse visualization of both mud-filtrate invasion and external/internal mudcake deposition. Our experimental method successfully examines the effects of rock heterogeneity, bedding plane orientation, and anisotropy on the spatial distribution of fluids and mudcake formation resulting from mud-filtrate invasion. It also emphasizes the importance of mud properties on the final fluid saturation state once mudcake seals the borehole. The procedure is fast, accurate, and reliable to quantify the process of mud-filtrate invasion at the core scale, enabling an improved understanding of invasion effects on borehole geophysical measurements following drilling operations, especially in spatially complex rocks such as laminated sandstones and carbonates.

High-Resolution X-Ray Radiography Methods Developed for Post-CHF Experiment

Radiation transmission measurement methods have become widely implemented in the study of two-phase flow due to leaping advancements in detector efficiency, spatial resolution, and high-speed measurement capabilities. However, radiation-based measurements of boiling experiments bear several challenges due to the mismatch of calibration to experimental conditions, beam hardening, thermal expansion, and material and working fluid density changes with temperature. The present research focuses on developing methods to analyze the high-resolution X-ray radiography measurements of the post-critical heat flux (Post-CHF) heat transfer facility built at the University of Michigan that is intended to perform high-pressure and high-temperature measurements; the experimental test section is made of Incoloy-800H and is characterized as a cylindrical geometry expanding 1.0 m in length. The broad goal of the experiment is to build a high-resolution database to develop models for inverted annular film boiling and inverted slug film boiling through dispersed flow film boiling. The methods developed in this research model the thermal effects of the postulated challenges in order to properly scale the X-ray calibration measurements to the experimental conditions. Additionally, a cross-section-weighted method is developed to estimate the axial void fraction; this method is validated by modeling the test section with synthetic void fraction data. Last, preliminary high-speed X-ray measurements performed at subcooled boiling conditions are presented and analyzed with the developed methods, which include bubbly, slug, and churn flows.

Fresnel zone plate point spread function approximation for zeroth order mitigation in millimetric field of view x-ray imaging.

High spatial and temporal resolution x-ray radiography images are required at the National Ignition Facility (NIF) for high-energy density experiments. One technique that is in development to achieve the required resolution uses Fresnel zone plate (FZP) optics to image an object that is backlit by an x-ray source. The multiple FZP diffraction orders do not focus on the same plane, which increases the background and reduces the contrast. Understanding the point spread function of the different diffraction orders will allow the prediction of the expected background using simulations. We find that the two-dimensional point spread function of the FZP can be approximated by the addition of a sharp Gaussian with a disk. This allowed for the estimation of the background in NIF experimental images of Rayleigh-Taylor spikes and their interpretation. An alternative design of FZP is discussed to allow the inclusion of a zeroth order blocker to reduce the background.

High-energy high-dose microfocus X-ray computed tomography driven by high-average-current photo-injector.

High-energy, high-dose, microfocus X-ray computed tomography (HHM CT) is one of the most effective methods for high-resolution X-ray radiography inspection of high-density samples with fine structures. Minimizing the effective focal spot size of the X-ray source can significantly improve the spatial resolution and the quality of the sample images, which is critical and important for the performance of HHM CT. The objective of this study is to present a 9 MeV HHM CT prototype based on a high-average-current photo-injector in which X-rays with about 70μm focal spot size are produced via using tightly focused electron beams with 65/66μm beam size to hit an optimized tungsten target. In digital radiography (DR) experiment using this HHM CT, clear imaging of a standard 0.1 mm lead DR resolution phantom reveals a resolution of 6 lp/mm (line pairs per mm), while a 5 lp/mm resolution is obtained in CT mode using another resolution phantom made of 10 mm ferrum. Moreover, comparing with the common CT systems, a better turbine blade prototype image was obtained with this HHM CT system, which also indicates the promising application potentials of HHM CT in non-destructive inspection or testing for high-density fine-structure samples.

X-ray imaging of Rayleigh-Taylor instabilities using Fresnel zone plate at the National Ignition Facility.

Being able to provide high-resolution x-ray radiography is crucial in order to study hydrodynamic instabilities in the high-energy density regime at the National Ignition Facility (NIF). Current capabilities limit us to about 20 μm resolution using pinholes, but recent studies have demonstrated the high-resolution capability of the Fresnel zone plate optics at the NIF, measuring 2.3 μm resolution. Using a zinc Heα line at 9 keV as a backlighter, we obtained a radiograph of Rayleigh-Taylor instabilities with a measured resolution of under 3 μm. Two images were taken with a time integrated detector and were time gated by a laser pulse duration of 600ps, and a third image was taken with a framing camera with a 100ps time gate on the same shot and on the same line of sight. The limiting factors on image quality for these two cases are the motion blur and the signal to noise ratio, respectively. We also suggest solutions to increase the image quality.

High-resolution x-ray radiography with Fresnel zone plates on the University of Rochester's OMEGA Laser Systems.

Experiments performed at the Laboratory for Laser Energetics with a continuous-wave (cw) x-ray source and on the OMEGA and OMEGA EP Laser Systems [Boehly et al., Opt. Commun. 133, 495 (1997) and Waxer et al., Opt. Photonics News 16, 30 (2005)] have utilized a Fresnel zone plate (FZP) to obtain x-ray images with a spatial resolution as small as ∼1.5 μm. Such FZP images were obtained with a charge-coupled device or a framing camera at energies ranging from 4.5 keV to 6.7 keV using x-ray line emission from both the cw source and high-intensity, laser-beam-illuminated metal foils. In all cases, the resolution test results are determined from patterns and grids backlit by these sources. The resolutions obtained are shown to be due to a combination of the spectral content of the x-ray sources and detector resolution limited by the magnification of the images (14× to 22×). High-speed framing cameras were used to obtain FZP images with frame times as short as ∼30 ps. Double-shell implosions on OMEGA were backlit by laser-irradiated Fe foils, thus obtaining a framing-camera-limited, FZP-image resolution of ∼3 μm-4 μm.

4D micro-scale, phase-contrast X-ray imaging and computed tomography of HMX-based polymer-bonded explosives during thermal runaway

High-resolution synchrotron x-ray radiography with computed tomography is used to observe the evolution of porosity created by thermal exposure in two HMX-based polymer-bonded explosive compositions; LX-04 and BX-63. The measurements were made in situ, over an extended period of time, during which the samples were heated on a slow-rate thermal trajectory. The tests ended with thermal-runaway to ignition after which the samples were consumed by combustion. The primary means of damage appears to be from mechanical debonding of the HMX-binder interface with secondary contribution from chemical decomposition. Confinement and binder properties affect the amount of porosity and permeability that develops. Additionally, observations were made describing the emergence and structure of an internal ignition volume, the formation and transport of a pre-ignition melt layer, and how the early stages of combustion were affected by material morphology, mechanical confinement and melt. The contact angle between molten HMX and the fluoropolymer, Viton A, is also presented. For the first time we have time-resolved x-ray images of ignition in sufficient detail to verify the mechanism of cookoff in polymer-bonded explosive compositions.

Observation of side arm splitting studied by high resolution X-ray radiography

Abstract The local dynamics of dendritic side arms during the growth stage were studied by in-situ radiography observations at high spatial resolution of better than 1 μm. A flat sample of a Ga–In alloy was solidified top-down applying a vertical temperature gradient. The evolving dendritic microstructure was visualized using synchrotron X-ray imaging at the beamline ID19 (ESRF, France). The experimental investigations on the dendrite evolution revealed a transition from a four-fold symmetry to a hyperbranched dendritic morphology. Both the side arm-splitting phenomenon – responsible for this morphological transition – as well as the arm growth dynamics were characterized using image processing.

Bremsstrahlung emission from high power laser interactions with constrained targets for industrial radiography

Laser–solid interactions are highly suited as a potential source of high energy X-rays for nondestructive imaging. A bright, energetic X-ray pulse can be driven from a small source, making it ideal for high resolution X-ray radiography. By limiting the lateral dimensions of the target we are able to confine the region over which X-rays are produced, enabling imaging with enhanced resolution and contrast. Using constrained targets we demonstrate experimentally a $(20\pm 3)~\unicode[STIX]{x03BC}\text{m}$ X-ray source, improving the image quality compared to unconstrained foil targets. Modelling demonstrates that a larger sheath field envelope around the perimeter of the constrained targets increases the proportion of electron current that recirculates through the target, driving a brighter source of X-rays.

Studying of Explosive Electron Emission From “Whisker” Cathode Using X-Ray Point-Projection Radiography

The results of direct observation of the initial phase of explosive electron emission using high-resolution X-ray radiography in X-pinch radiation are reported. The confirmation of common “Ecton” theory was not found within achieved temporal and spatial resolutions. A mechanism involving the surface breakdown of whiskers that leads to plasma development is proposed.

Mass transfer measurement in a square milli-channel and comparison with results from a circular channel

In this work, we report on an experimental investigation of mass transfer from stagnant Taylor bubbles in a small square channel via measurement of the dissolution rate of an individual elongated bubble of carbon dioxide into water. As a measurement technique we used high resolution X-ray radiography and tomography. The changes in the size of the bubble at constant pressure obtained from the high-resolution X-ray images were used to calculate the liquid side mass transfer coefficient. The bubbles were continuously monitored by hydrodynamic fixation of the bubble in a down flow of the liquid. The results are compared with the available recently published data for circular channels.The results show that the bubble dissolution curves in square channels are relatively even while the dissolution curves for bubbles in circular channels show some noticeable change in the slope. Furthermore, it is shown that the calculated liquid side mass transfer coefficient based on the measured data show good agreement with the data predicted by the penetration theory when the contact time between two phases is defined as the ratio of bubble length to the relative velocity. In addition, the comparison of the results with the data for circular channels showed that despite the fact that the rise velocity of bubbles in square channel is about three times faster than in circular channel, the liquid side mass transfer coefficients are approximately the same.

High-resolution X-ray projection radiography of a pin cathode in a high-current vacuum diode using X-pinch radiation

To study processes in a high-current vacuum diode with a cathode in the form of a single pin made of a metallic wire 20–30 μm in diameter, the method of high-resolution projection X-ray radiography with an X-pinch as a source has been used. A strong inhomogeneity of the energy contribution to the wire has been revealed. The smallest energy release has been observed near the end of the pin, where the electric field strength is maximal. Hard X rays, as well as the ejection of matter from the anode, have been observed, indicating the generation of an electron beam with the parameters characteristic of explosive electron emission in the diode with this configuration. The data obtained indicate complex processes occurring in the diode. Possible scenarios of their development have been considered.

Experimental Studies of Hollow Structure Formed in the Dense Core of Exploded Wires

Complex hollow structures have been observed in the cores of single exploded wires and multiwire arrays using high-resolution X-ray radiography and laser probing. The radiographs show features supporting earlier research that suggested the core is a foamlike liquid–vapor mixture.

High spectral and spatial resolution X-ray transmission radiography and tomography using a Color X-ray Camera

High resolution X-ray radiography and computed tomography are excellent techniques for non-destructive characterization of an object under investigation at a spatial resolution in the micrometer range. However, as the image contrast depends on both chemical composition and material density, no chemical information is obtained from this data. Furthermore, lab-based measurements are affected by the polychromatic X-ray beam, which results in beam hardening effects. New types of X-ray detectors which provide spectral information on the measured X-ray beam can help to overcome these limitations. In this paper, an energy dispersive CCD detector with high spectral resolution is characterized for use in high resolution radiography and tomography, where a focus is put on the experimental conditions and requirements of both measurement techniques.

Visualization of Liquid Water Accumulation in PEMFCs Operating at Different Temperatures by Soft X-ray Radiography

In situ observation of liquid water accumulation in PEMFCs operating at 30ºC, 50ºC, and 70ºC was performed by using high-resolution soft X-ray radiography. A less amount of liquid water in the MPL and GDL was observed in the elevated operating temperature. It is suggested that water generated in the electrode is mainly transported as vapor at higher temperature conditions investigated. The liquid water accumulation was significantly smaller in the MPL than in the GDL, independently observed in all operating temperature.

X-ray radioscopy in-situ studies in thermoplastic polymer foams

The current work addresses results on two types of in-situ studies: bubble nucleation/growth and bubble coalescence for two thermoplastic materials (polypropylene and polyethylene) foamed by a chemical blowing agent (azodicarbonamide) under varying temperature conditions. The foaming process of these high viscosity materials has been in-situ monitored for the first time using a high resolution X-ray radiography set up. The studies were carried out in specially designed X-ray transparent furnaces reaching temperatures over the melting point of the polymer and the decomposition temperature of the blowing agent (which generates the expanding gas). Sequences of radiographies were typically acquired at 0.5Hz. Image processing allowed evaluating several foam features such as cell nucleation rate and coalescence detection/quantification. Results on pore nucleation and growth indicate a high influence of heating rate for this variable and reveal an apparent competition between pore growth velocity and the number of nucleated pores. Results on cell coalescence highlight special features of this highly viscous systems in comparison to low viscosity ones (aqueous and metallic foams). Ruptures in these materials take much longer times (up to 10s) and generate a large interaction with the surrounding cells making more difficult the quantification of the process.

Observation of dynamic liquid water transport in the microporous layer and gas diffusion layer of an operating PEM fuel cell by high-resolution soft X-ray radiography

In-situ observation of liquid water transport in the microporous layer (MPL) and gas diffusion layer (GDL) of an operating proton exchange membrane fuel cell (PEMFC) was performed using high-resolution soft X-ray radiography. The amount of liquid water accumulated in the MPL and GDL increases with increasing in current density. The amount of liquid water in the MPL is low near the catalyst layer and higher toward the GDL side. The liquid water is transported to the GDL mainly through the cracks in the MPL. The dynamic liquid water transport from the cracks in the MPL to the interconnected pores in the GDL was observed.