We are reporting novel thin-film scintillators using nanomaterials of a transparent boron compound (10B enriched) embedded in an organic or inorganic phosphor matrix. In comparison to the 6LiF/ZnS and 6LiF/gadolinium oxysulfide scintillators, the new scintillator has a much higher neutron absorption cross-section and a much lower x-ray/gamma ray sensitivity. Moreover, the fluorescent decay constant of our organic phosphor (~ns) is much shorter than the commercial scintillators (~ µs) that can potentially benefit neutron multiplicity counting to detect and quantify nuclear materials in safeguards, arms control, and emergency response. Due to the reinforcement of the boron nanomaterials, the scintillator thin films with organic and inorganic phosphors are both mechanically robust and can be made ultra-thin and flexible. Those new properties will allow them to conformally adhere to irregularly shaped imaging objects, leading to an improved spatial resolution for future neutron radiography.
Nuclear voltaic batteries are not a new concept, yet their advancement is hindered by low power conversion efficiency and low power output. An alternative method to integrating a radioisotope with a semiconductor energy transducer for power generation involves capturing gamma rays with a bulk scintillator, which then converts the resulting visible light directly to electricity through commercially available solar cells. This approach is referred to as a nuclear photovoltaic battery which targets external radiation fields such as waste storage or areas close to high-intensity gamma-ray emitters. We explored this concept using a 2cm x 2cm x 1cm Gadolinium Aluminum Gallium Garnet (GAGG:Ce (HL)) scintillator, a polycrystalline CdTe solar cell with an Au contact size of 1.3cm x 1.3cm, and a high gamma field emitted by a Cs-137 (~1.5 kRad/hr) irradiator. The preliminary measurements yielded a maximum power output of ~ 280nW, with open circuit voltage (Voc) and short circuit current (Isc) of 0.34V and 1.98μA, respectively, resulting in a Fill Factor of 41.5%.
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.
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.
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.
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.
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.
Polyvinyl Toluene (PVT) based plastic scintillators with varying dimensions and fluors have been characterized in terms of relative light output and spatial resolution. Scintillators were exposed to fast neutrons (~2 MeV), and images were obtained with a setup consisting of an EMCCD camera, a mirror and a light-tight apparatus. Among scintillators with 2.0% Flrpic and 10.16 cm (4 inch) diameter, the 10.5-mm thick scintillator featured the highest light output while 3.0- mm provided the best spatial resolution. The deuterated 3.0-mm thick scintillator doped with 2.0% Flrpic showed a worse performance in terms of both light output and spatial resolution compared to that of undeuterated scintillator with the same thickness but doped with 2.0% X-Flrpic. This study reveals the effects of presence of deuterium in PVT, the thickness of scintillator, and the fluor on the light output and spatial resolution of plastic scintillator.
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