Frequency modulated continuous wave (FMCW) radar in the K-band has been shown to be an effective detector of geomaterial physical properties being highly sensitive to rock characteristics, ...particularly mineral composition and, for porous rock, variations in liquid water content. This research demonstrates that contrasts in FMCW return signals with time correlate with changes in geomaterial water content. FMCW signal returns were acquired for porous sandstone samples subjected to controlled water injection while also in a neutron beam, taking advantage of the well-known, and well-calibrated, attenuation of neutrons by hydrogen atoms for the water-containing porous sandstone samples. The sequential neutron tomographic images clearly show water moving up the sample with time while the FMCW observations show increases in radar reflection coefficient as a function of water position in the field of view. The observed FMCW detection of flood-front position is corroborated by the synchronous neutron tomographic images. We also observe repeatable variations in the radar reflection coefficient as a function of sample orientation during fluid injection, verifying that FMCW sensing offers real-time insight into the interactions between fluid movement and sample heterogeneity, via non-contact and non-invasive flood-front tracking. This research demonstrates that FMCW has potential to be a more accessible and easily deployable sensing modality than neutron tomography, enabling dynamic geomaterial testing to be conducted outwith the confines of the highly controlled laboratory environment required for neutron investigation.
In this work, a new dual modality monitoring technique is presented to demonstrate its interest to investigate the salt precipitation dynamics induced by gas flow-through drying. It consists of ...imaging simultaneously a core flood using both Neutron and X-ray beams. A method to calibrate and process the two signals is presented. It takes advantage of the difference in attenuation between the two ionizing radiations to quantify the different phase saturations and compositions as well as the reduction of porosity caused by salt precipitation. A set of experiments has been conducted at the NeXT-Grenoble beamline of the
Institute Laue-Langevin
facilities (
ILL
, France). Experiments were conducted on a homogeneous rock sample of Bentheimer sandstone using dry nitrogen and a 100 g/L KBr brine. The two first experiments aimed to calibrate the dual modality for the different phases. The last two experiments have been conducted with a brine capillary contact maintained at the gas outlet. Experimental data have given new insights into the organization of the three phases (the brine, the gas, and the precipitated salt) when a salt bank is formed in the sample. These quantities computed using dual-modality imaging show great similarities with published work. The salt accumulation was used to estimate the flow rate of brine pumped through the capillary contact to compensate for the brine evaporation in the gas phase. Observations have shown that a reduction of the initial porosity in some sections of the sample by 12–14% was enough to trigger a gas draw-down characterized by the migration of the salt toward the gas inlet. In some conditions (low gas inlet pressure for example), the rise of the water could be fast enough to form a second salt bank higher in the sample. It has been observed that the formation of the second salt bank could spread the precipitated salt in a less damaging configuration for the gas flow, triggering a phase of gas build-up characterized by the withdrawal of the water. These phases of gas draw-down and build-up could alternate until the sample clogs.
In digital neutron imaging, the neutron scintillator screen is a limiting factor of spatial resolution and neutron capture efficiency and must be improved to enhance the capabilities of digital ...neutron imaging systems. Commonly used neutron scintillators are based on
LiF and gadolinium oxysulfide neutron converters. This work explores boron-based neutron scintillators because
B has a neutron absorption cross-section four times greater than
Li, less energetic daughter products than Gd and
Li, and lower γ-ray sensitivity than Gd. These factors all suggest that, although borated neutron scintillators may not produce as much light as
Li-based screens, they may offer improved neutron statistics and spatial resolution. This work conducts a parametric study to determine the effects of various boron neutron converters, scintillator and converter particle sizes, converter-to-scintillator mix ratio, substrate materials, and sensor construction on image quality. The best performing boron-based scintillator screens demonstrated an improvement in neutron detection efficiency when compared with a common
LiF/ZnS scintillator, with a 125% increase in thermal neutron detection efficiency and 67% increase in epithermal neutron detection efficiency. The spatial resolution of high-resolution borated scintillators was measured, and the neutron tomography of a test object was successfully performed using some of the boron-based screens that exhibited the highest spatial resolution. For some applications, boron-based scintillators can be utilized to increase the performance of a digital neutron imaging system by reducing acquisition times and improving neutron statistics.
Neutron tomography has emerged as a promising imaging technique for specific applications in bone research. Neutrons have a strong interaction with hydrogen, which is abundant in biological tissues, ...and they can penetrate through dense materials such as metallic implants. However, in addition to long imaging times, two factors have led to challenges in running
in situ
mechanical characterization experiments on bone tissue using neutron tomography: 1) the high water content in specimens reduces the visibility of internal trabecular structures; 2) the mechanical properties of bone are dependent on the hydration state of the tissue, with drying being reported to cause increased stiffness and brittleness. This study investigates the possibility of improving image quality in terms of neutron transmission and contrast between material phases by drying and rehydrating in heavy water. Rat tibiae and trabecular bovine bone plugs were imaged with neutron tomography at different hydration states and mechanical testing of the bone plugs was carried out to assess effects of drying and rehydration on the mechanical properties of bone. From analysis of image histograms, it was found that drying reduced the contrast between bone and soft tissue, but the contrast was restored with rehydration. Contrast-to-noise ratios and line profiles revealed that the contrast between bone tissue and background was reduced with increasing rehydration duration but remained sufficient for identifying internal structures as long as no free liquid was present inside the specimen. The mechanical analysis indicated that the proposed fluid exchange protocol had no adverse effects on the mechanical properties.
X-ray and neutron imaging are widely employed for battery materials, thanks to the possibility to perform noninvasive
in situ
and
in operando
analyses. X-ray tomography can be performed either in ...synchrotron or in laboratory facilities and is particularly well-suited to analyze bulk materials and electrode/electrolyte interfaces. Several post-lithium-ion (Li-ion) devices, such as Li–sulfur, Li–O
2
, or all-solid-state Li batteries, have an anode made of metallic Li in common. The main failure mode of Li batteries is the inhomogeneity of the Li electrodeposits onto the Li anode during charge steps, leading to dendrite growth and low Coulombic efficiency. X-ray tomography is a powerful tool for studying dendrites as it provides useful information about their locations, dynamics, and microstructures. So far, the use of neutron tomography is scarcely reported for Li deposit analysis due to the difficulty in reaching sufficient image resolution to capture the deposit microstructure, that is, typically below 10–20 µm. The very different interactions of X-rays and neutrons with Li, which has significantly different opacity in the two cases, make the two techniques highly complementary. Notably, the capacity of neutrons to discern different Li isotopes is pivotal to getting an insight into the composition of Li deposits by distinguishing between Li originating from an electrode (
6
Li in this study) and Li originating from the Li salt electrolyte (mainly in
7
Li here). Indeed, the theoretical linear neutron attenuation coefficient of
6
Li is about 15 and 2,000 times larger than that of natural Li and
7
Li, respectively. Therefore, a high imaging contrast difference is obtained between
6
Li (high attenuation) and natural Li and
7
Li (lower attenuations), which could allow a better understanding of the origin of the Li comprising the electrodeposits. In this work, we report, as a proof of concept, an
in situ
neutron tomography imaging of Li electrodeposits in a cycled Li symmetric cell. The electrochemical cell comprises a natural Li electrode, a
6
Li electrode, and a deuterated liquid electrolyte. The neutron tomographies are compared with X-ray tomography images of the same electrochemical cell acquired both at an X-ray synchrotron beamline and at a laboratory X-ray tomograph. Neutron tomography is shown to be compatible with
in situ
analysis and capable of capturing the overall morphology of the Li deposits in good accordance with X-ray tomography analyses.
Abstract Water management plays a key role in ensuring optimum polymer electrolyte fuel cell (PEFC) performance, and flow field design can influence the ability of a cell to balance maintaining ...hydration, whilst avoiding flooding and cell failure. This work deepens the understanding of water evolution in different PEFC flow channel designs, namely single serpentine (SS), double serpentine (DS) and parallel, using our novel high-speed neutron computed tomography method. We developed our previously-reported method by introducing continuous cell rotation, enabling 18 s per tomogram during 1 h holds at 300, 400 and 500 mA cm −2 . The volume of water evolved in the cathode, membrane electrode assembly and anode was quantified, and key mechanisms for water droplet formation in the different flow channel designs were elucidated. The parallel flow field design had the poorest water management, with 47% of the cathode flow channel becoming filled after 1 h at 400 mA cm −2 . This significant flooding blocked reactant sites and contributed to unstable cell performance and, ultimately, cell failure at higher current densities. The SS cell displayed the best water management, with only 11% of the cathode channel filled with water after 1 h at 500 mA cm −2 , compared with 28% of the DS cathode channel. 3D visualisation and analysis of droplet behaviour elucidated how water ‘slugs’ in the SS were removed in the gas stream, whereas three of the four parallel cathode flow channels became entirely filled with water plugs, blocking gas flow and exacerbating cell flooding. The new insights gained here are expected to extend to novel flow field designs and image-based models, with the use of operando neutron CT demonstrated as a powerful technique for both visualising and quantifying water management in operating PEFCs, as well as deepening the knowledge of droplet behaviour in different flow field types.
The behaviour of subsurface-reservoir porous rocks is a central topic in the resource engineering industry and has relevant applications in hydrocarbon, water production, and CO2 sequestration. One ...of the key open issues is the effect of deformation on the hydraulic properties of the host rock and, specifically, in saturated environments. This paper presents a novel full-field data set describing the hydro-mechanical properties of porous geomaterials through in situ neutron and X-ray tomography. The use of high-performance neutron imaging facilities such as CONRAD-2 (Helmholtz-Zentrum Berlin) allows the tracking of the fluid front in saturated samples, making use of the differential neutron contrast between "normal" water and heavy water. To quantify the local hydro-mechanical coupling, we applied a number of existing image analysis algorithms and developed an array of bespoke methods to track the water front and calculate the 3D speed maps. The experimental campaign performed revealed that the pressure-driven flow speed decreases, in saturated samples, in the presence of pre-existing low porosity heterogeneities and compactant shear-bands. Furthermore, the observed complex mechanical behaviour of the samples and the associated fluid flow highlight the necessity for 3D imaging and analysis.
Corrosion of reinforcing bars constitutes the largest threat to the durability of concrete structures. Thus, several studies have investigated the nature of the corrosion products, most using ...post-mortem analyses. However, corrosion products evolve when in contact with oxygen, hindering result interpretation. This work presents instead a state-of-the-art, non-destructive 3D method for the assessment of corrosion of embedded reinforcements.
Multimodal neutron and X-ray tomography was used to observe, non-destructively, the characteristics of the corrosion products in two concrete samples, with the aim of investigating possible benefits of the use of this technique for reinforced concrete structures. One sample was naturally corroded, extracted from an 81-year-old bridge, the other was corroded via the galvanostatic method, resulting in corrosion-induced cracks. Quantitative and qualitative data was acquired, including the iron-to-rust volumetric ratio in macroscopic interfacial voids and the thickness of the corrosion layer at the steel concrete interface. The iron-to-rust volumetric ratio corresponded to large, soluble, corrosion products, forming in environments with low availability of oxygen for both samples.
Understanding fluid flow in rocks is crucial to quantify many natural processes such as ground water flow and naturally triggered seismicity, as well as engineering questions such as displacement of ...contaminants, the eligibility of subsurface waste storage, geothermal energy usage, oil and gas recovery and artificially induced seismicity. Two key parameters that control the variability of fluid flow and the movement of dissolved chemical species are (i) the local hydraulic conductivity, and (ii) the local sorption properties of the dissolved chemical species by the solid matrix. These parameters can be constrained through tomography imaging of rock samples subjected to fluid injection under constrained flow rate and pressure. The neutron imaging technique is ideal to explore fluid localization in porous materials due to the high but variable sensitivity of neutrons to the different hydrogen isotopes. However, until recently, this technique was underused in geology because of its large acquisition time. With the improved acquisition times of newly set-up neutron beamlines, it has become easier to study fluid flow. In the current set of experiments, we demonstrate the feasibility of in-situ 2D and 3D time-lapse neutron imaging of fluid and pollutant percolation in rocks, in particular that of cadmium salt. Cadmium is a hazardous compound that is found in many electronic devices, including batteries and is a common contaminant in soil and groundwater. It also exhibits higher contrast in neutron attenuation with respect to heavy water, and is therefore an ideal tracer. Time-lapse 2D radiographies and 3D neutron tomographies of the samples were acquired on two neutron beamlines (ILL, France and SINQ, Switzerland). We performed two sets of experiments, imbibition and injection experiments, where we imaged in-situ flow properties, such as local permeability and interactions between cadmium and the solid rock matrix. Our results indicate that even within these cm-scale porous rocks, cadmium transport follows preferential pathways, and locally interacts within the limestone samples. Our results demonstrate that the use of neutron imaging provides additional insights on subsurface transport of pollutants.
NeXT-Grenoble, the Neutron and X-ray tomograph in Grenoble Tengattini, Alessandro; Lenoir, Nicolas; Andò, Edward ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2020, Letnik:
968
Journal Article
Recenzirano
Odprti dostop
NeXT-Grenoble is a Neutron and X-ray Tomograph launched from the collaboration between the Universite Grenoble Alpes (UGA) and the Institut Laue Langevin (ILL). The design started in February 2016 ...shortly followed by its construction at ILL. A first version of the instrument has been opened to users since October 2016.
One of the peculiarities of the instrument is that, as suggested by the name, the instrument allows the acquisition of truly simultaneous Neutron and X-ray tomographies, taking advantage of the high complementarity of these two beams.
Also by virtue of the uniquely high flux at the ILL, the instrument can provide unprecedented spatial resolution (around 4μm true resolution, in few tens of seconds) and acquisition speed (1.5 s tomographies).
This contribution details the adopted technical solutions and performances achieved, reviews some of the key published results and outlines the future direction of the instrument.
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