Imaging stitching is a solution for radiography and computed tomography (CT) applications where the object is larger than the beam size. Imaging stitching algorithms require a robust noise filter that maintains the landmark features used in stitching. In lens-coupled neutron radiography and CT, a camera is placed away from the neutron beam. Even with shielding, the camera experiences a high radiation dose of mixed gammas and neutrons. The CCD silicon sensor, sensitive to both gammas and neutrons, introduces speckled noise, pixel oversaturation, and blooming effects. Conventional median filters prove inadequate with this type of noise and can result in blurred images. Manual filtering of CT sets is time-consuming and error-prone. An improved image filtering method designed for neutron CT data sets is therefore needed to improve imaging stitching algorithms. We have developed a method that utilizes statistical information in radiographs and variable-sized radii filtration to adequately remove noise while preserving resolution. Once noise has been identified, the algorithm tracks cluster size to inform local filter needs. Filtered radiographs are stitched using a semi-automatic algorithm. This approach works best for data containing features for joint corner detection. It does require specific user inputs, such as object size, features of interest, and alignment, to pinpoint the optimal joining location. Overall, our method represents a significant advancement in neutron CT image processing, offering improved results for imaging stitching and traditional CT applications. We describe the application of this combined filter and stitching algorithm on thermal and fast neutron CT data at OSURR.
Neutron Depth Profiling (NDP) is an analytical neutron technique that continues to grow in popularity for the quantification of Li ions in lithium-ion battery (LIB) materials. Most investigations occur at high flux neutron sources, i.e. cold or thermal neutron beam facilities, offered by high-power (10-20 MW) research reactors and employing multiple NDP energy and concentration standards. This work aims to develop a feasible method using NDP facilities with less intense neutron flux at lower power research reactors to quantitatively determine the Li concentration in LIB materials, while also applying a “thick” energy and concentration standard. Here, we describe a methodology for processing and calibrating NDP data collected using a multi-detector (i.e., 7-detector setup), which is essential to increase the detection efficiency. The Li concentration of a Li6PS5Cl0.5Br0.5 solid-state electrolyte was determined to be 2.2×1022 Li atoms cm−3. This value deviated by less than 3% of the expected Li atom concentration using a “thick” LiF single crystal wafer as a concentration standard. The method described in this work can be applied to other low-power reactors and other NDP-sensitive isotopes to further increase the application and availability of user-based NDP facilities.
Neutron radiography and computed tomography may be used to investigate internal structures of complex multi-material objects nondestructively. Thermal neutrons are more effective at producing high-contrast radiographs of objects composed of elements with relatively low atomic numbers (Z). A capability to produce high-quality CT reconstructions from both thermal and fast neutron computed tomography (nCT) using a lens-coupled imaging was demonstrated using various Additively Manufactured (AM’d) and Electrical Discharge Machining (EDM) phantoms, with layers and distinct features, made with intentional voids and out of high- and low-Z elements.
X-ray computed tomography (CT)systems can produce high resolution images, in which small (sub-millimeter) features can be detected. This requires the X-rays to sufficiently penetrate the object and interact strongly enough to produce measurable attenuation. Low atomic number (low Z), low density objects shielded by high atomic number (high Z) materials result in X-ray reconstructions that lack sufficient contrast to differentiate interior features from noise and reconstruction artifacts. Fast neutron CT offers complementary information to X-rays with superior penetration through high Z shielding and with less severe beam hardening artifacts. However, spatial resolution in X-ray imaging systems is generally superior to that of fast neutron imagers. Here, we quantitatively compare these two complementary modalities to demonstrate the ability to observe small feature locations within two multi-material objects. Quantitative measures include calculation of image gradient at material edges, contrast-to-noise ratio, and F1 score.
Fast neutron Computed Tomography (nCT) is a powerful and non-invasive imaging modality that can be used to examine features and defects within low Z elements (such as plastic) hidden or shielded by high Z elements (such as tungsten, lead, or even stainless steel). This study built a fast neutron radiography and nCT system and explored various multi-material complex objects utilizing a fast neutron beam at The Ohio State University Research Reactor (OSURR), which provides ~5.4 x 10^7 n·cm-2·s-1 neutron flux at 1.6 MeV (median energy). The lens-based system includes an Electron Multiplying (EM) CCD camera, a light-tight enclosure, and a high light yield 1 cm thick Polyvinyl Toluene (PVT) scintillator provided by Lawrence Livermore National Laboratory (LLNL). A variety of test exemplars were scanned, with the number of projections for each scan ranging from 90 to 180, covering either 180 or 360 degrees. The exposure time for each projection ranged down to one minute, enabling a full nCT scan within a few hours of operation at a 500-kW low power research reactor. 3D tomograms were constructed using Octopus reconstruction software. Results showed that not only could nCT projection data be successfully constructed into volume data, but good contrast between HDPE and a millimeter-sized tungsten ball could be obtained. The 3D tomography presents high contrast to clearly discern HDPE features and voids inside tungsten shielding that are not discernable using 2D radiography.
Automation and remote control are added to a fast neutron tomography system at the Ohio State University Research Reactor (OSURR). The automated system with XYZ stages allows for an improved imaging efficiency and quality of computed tomography, while reducing total image acquisition time and keeping the user further from the neutron beam facility. The automation code was written in Python scripting utilizing the Tkinter GUI structure and modules for instrumentation control. A Python wrapper for Micro-Manager, pycromanager, is used to control the Electron Multiply (EM) CCD and CMOS cameras. The system has a three directional XYZ stage for precise alignment and a rotational stage to obtain the radiograph views for computed tomography. Both of these stages hold the imaging object and are external to the light tight box. Finally, another one direction stage is employed within the light tight box to move the camera for real-time focusing. Each stage is controlled through user defined functions that pull from the serial control offered by pyserial. Within the light tight box is the camera, a telecentric lens, a mirror, and a Polyvinyl Toluene (PVT) scintillator. The GUI allows for the users to input all of the experiment parameters such as exposure time, EM Gain (for EMCCD), file save information, and rotational requirements. Upon submission, the rotational degree information is passed into an algorithm to generate a list for a few view tomography. As the imaging system takes and saves the images, the users are shown the progress in real time through messages and pictures in the GUI.
High energy X-rays and neutrons can provide 3-D volumetric views of large objects made of multiple materials. Lenscoupled computed tomography using a scintillator imaged on a CCD camera obtains high spatial resolution, while a surface-mounted segmented scintillator on an amorphous silicon (A-Si) array can provide high throughput. For MeV Xray CT, a new polycrystalline transparent ceramic scintillator referred to as “GLO” offers excellent stopping power and light yield for improved contrast in sizes up to a 12” field-of-view. For MeV neutron CT, we have fabricated both contiguous and segmented plates of “Hi-LY” plastic scintillator, offering light yields 3x higher than standard plastic.
The Ohio State University Research Reactor's (OSURR) fast neutron beamline is aimed to meet the growing demand for high flux and well-collimated neutron sources for fast neutron radiography and tomography applications. The beam facility consists of two collimators, separated by a neutron-gamma shutter, and a movable beam stop, sitting on a rail system for back/forth and up/down motion to provide an adjustable working space. The beam facility provides a beam diameter of 3.2-cm and has a calculated geometric L/D ratio of ~62. The collimator closer to reactor core includes a 10.16-cm thick polycrystalline Bismuth for filtering gamma-rays, which provides ~2 orders of magnitude reduction in gamma flux at 2-MeV, and a 15.24-cm thick graphite with a 3.2-cm diameter aperture. Various Monte Carlo N-Particle (MCNP) simulations were performed to obtain neutron energy spectrum, neutron and gamma flux distributions, and dose rate values. Simulations showed a fast neutron (@1.6 MeV) flux ~5.4 × 107 n·cm-2·s-1 at the collimator exit. While the simulations of neutron and gamma flux distributions have verified that the beam shutter and beam stop provide a decent neutron and gamma shielding, a neutron radiograph of the beam was experimentally obtained using a Polyvinyl Toluene (PVT) based plastic scintillator and a lens-based imaging setup which has further validated the simulated radiographs of the beam. Simulations also provided neutron dose rates around the beam stop with a close agreement with experimental values. However, disagreements were found between experimental and simulated gamma flux dose rates, which needs further validation.
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