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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Scientific Computational Imaging Code (SCICO)

Scientific Computational Imaging Code (SCICO) is a Python package for solving the inverse problems that arise in scientific imaging applications. Its primary focus is providing methods for solving ill-posed inverse problems by using an appropriate prior model of the reconstruction space. SCICO includes a growing suite of operators, cost functionals, regularizers, and optimization routines that may be combined to solve a wide range of problems, and is designed so that it is easy to add new building blocks. SCICO is built on top of JAX rather than NumPy, enabling GPU/TPU acceleration, just-in-time compilation, and automatic gradient functionality, which is used to automatically compute the adjoints of linear operators. An example of how to solve a multi-channel tomography problem with SCICO is shown in Figure 1. The SCICO source code is available from GitHub, and pre-built packages are available from PyPI. It has extensive online documentation, including API documentation and usage examples, which can be run online at Google Colab and binder.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Genetic algorithms applied to reconstructing coded imaging of neutrons and analysis of residual watermark

Monte-Carlo simulation of neutron coded imaging based on encoding aperture for Z-pinch of large field-of-view with 5 mm radius has been investigated, and then the coded image has been obtained. Reconstruction method of source image based on genetic algorithms (GA) has been established. 'Residual watermark,' which emerges unavoidably in reconstructed image, while the peak normalization is employed in GA fitness calculation because of its statistical fluctuation amplification, has been discovered and studied. Residual watermark is primarily related to the shape and other parameters of the encoding aperture cross section. The properties and essential causes of the residual watermark were analyzed, while the identification on equivalent radius of aperture was provided. By using the equivalent radius, the reconstruction can also be accomplished without knowing the point spread function (PSF) of actual aperture. The reconstruction result is close to that by using PSF of the actual aperture.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

A hybrid of fractal image coding and fractal dimension for an efficient retrieval method

Fractal image coding (FIC) based on the inverse problem of an iterated function system plays an essential role in several areas of computer graphics and in many other interesting applications. Through FIC, an image can be transformed to compressed representative parameters and be expressed in a simple geometric way. Dealing with digital images requires storing a large number of images in databases, where searching such databases is time consuming. Therefore, finding a new technique that facilitates this task is a challenge that has received increasing attention from many researchers. In this study, a new method that combines fractal dimension (FD) which is an indicator of image complexity with the FIC scheme is proposed. Classifying images in databases according to their texture by using FD helps reduce the retrieval time of query images. The validity of the proposed method is evaluated using geosciences images. Result shows that the method is computationally attractive.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Synthetic Diagnostics Platform for Fusion Plasma and a Two-Dimensional Synthetic Electron Cyclotron Emission Imaging Code

Magnetic confinement fusion is one of the most promising approaches to achieve fusion energy. With the rapid increase of the computational power over the past decades, numerical simulation have become an important tool to study the fusion plasmas. Eventually, the numerical models will be used to predict the performance of future devices, such as the International Thermonuclear Experiment Reactor (ITER) or DEMO. However, the reliability of these models needs to be carefully validated against experiments before the results can be trusted. The validation between simulations and measurements is hard particularly because the quantities directly available from both sides are different. While the simulations have the information of the plasma quantities calculated explicitly, the measurements are usually in forms of diagnostic signals. The traditional way of making the comparison relies on the diagnosticians to interpret the measured signals as plasma quantities. The interpretation is in general very complicated and sometimes not even unique. In contrast, given the plasma quantities from the plasma simulations, we can unambiguously calculate the generation and propagation of the diagnostic signals. These calculations are called synthetic diagnostics, and they enable an alternate way to compare the simulation results with the measurements. In this dissertation, we present a platform for developing and applying synthetic diagnostic codes. Three diagnostics on the platform are introduced. The reflectometry and beam emission spectroscopy diagnostics measure the electron density, and the electron cyclotron emission diagnostic measures the electron temperature. The theoretical derivation and numerical implementation of a new two dimensional Electron cyclotron Emission Imaging code is discussed in detail. This new code has shown the potential to address many challenging aspects of the present ECE measurements, such as runaway electron effects, and detection of the cross phase between the electron temperature and density fluctuations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Advanced Imaging Optics Utilizing Wavefront Coding

Image processing offers a potential to simplify an optical system by shifting some of the imaging burden from lenses to the more cost effective electronics. Wavefront coding using a cubic phase plate combined with image processing can extend the system's depth of focus, reducing many of the focus-related aberrations as well as material related chromatic aberrations. However, the optimal design process and physical limitations of wavefront coding systems with respect to first-order optical parameters and noise are not well documented. We examined image quality of simulated and experimental wavefront coded images before and after reconstruction in the presence of noise. Challenges in the implementation of cubic phase in an optical system are discussed. In particular, we found that limitations must be placed on system noise, aperture, field of view and bandwidth to develop a robust wavefront coded system.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Random mask optimization for fast neutron coded aperture imaging

In coded aperture imaging, one of the most important factors determining the quality of reconstructed images is the choice of mask/aperture pattern. In many applications, uniformly redundant arrays (URAs) are widely accepted as the optimal mask pattern. Under ideal conditions, thin and highly opaque masks, URA patterns are mathematically constructed to provide artifact-free reconstruction however, the number of URAs for a chosen number of mask elements is limited and when highly penetrating particles such as fast neutrons and high-energy gamma-rays are being imaged, the optimum is seldom achieved. In this case more robust mask patterns that provide better reconstructed image quality may exist. Through the use of heuristic optimization methods and maximum likelihood expectation maximization (MLEM) image reconstruction, we show that for both point and extended neutron sources a random mask pattern can be optimized to provide better image quality than that of a URA.

McMillan, Kyle↗
DOE OSTI2018

Effects of Magnetic and Electric Field Uniformity on Coded Aperture Imaging Quality in a Cycloidal Mass Analyzer

Cycloidal mass analyzers are unique sector mass analyzers as they exhibit perfect double focusing, making them ideal for incorporating spatial aperture coding, which can increase the throughput of a mass analyzer without affecting the resolving power. However, the focusing properties of the cycloidal mass analyzer depend on the uniformity of the electric and magnetic fields. In this paper, finite element simulation and charged particle tracing were used to investigate the effect of field uniformity on imaging performance of a cycloidal mass analyzer. For the magnetic field, we evaluate a new permanent magnet geometry by comparing it to a traditional geometry. Results indicate that creating an aperture image in a cycloidal mass spectrometer with the same FWHM as the slit requires less than 1% variation in magnetic field strength along the ion trajectories. The new magnet design, called the opposed dipole magnet, has less than 1% field variation over an area approximately 62 × 65 mm; nearly twice the area available in a traditional design of similar size and weight. This allows ion imaging across larger detector arrays without loss of resolving power. In addition, we compare the aperture imaging quality of a traditionally used cycloidal mass spectrometer electric design with a new optimized design with improved field uniformity. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Coherent diffractive imaging using randomly coded masks

We experimentally demonstrate an extension to coherent diffractive imaging that encodes additional information through the use of a series of randomly coded masks, removing the need for typical object-domain constraints while guaranteeing a unique solution to the phase retrieval problem. Phase retrieval is performed using a numerical convex relaxation routine known as “PhaseCut,” an iterative algorithm known for its stability and for its ability to find the global solution, which can be found efficiently and which is robust to noise. The experiment is performed using a laser diode at 532.2 nm, enabling rapid prototyping for future X-ray synchrotron and even free electron laser experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Correlated Statistical Uncertainties in Coded-Aperture Imaging

In nuclear security applications, coded-aperture imagers provide the opportu- nity for a wealth of information regarding the attributes of both the radioac- tive and non-radioactive components of the objects being imaged. However, for optimum benefit to the community, spatial attributes need to be deter- mined in a quantitative and statistically meaningful manner. To address the deficiency of quantifiable errors in coded-aperture imaging, we present uncer- tainty matrices containing covariance terms between image pixels for MURA mask patterns. We calculated these correlated uncertainties as functions of variation in mask rank, mask pattern over-sampling, and whether or not anti- mask data are included. Utilizing simulated point source data, we found that correlations (and inverse correlations) arose when two or more image pixels were summed. Furthermore, we found that the presence of correlations (and their inverses) was heightened by the process of over-sampling, while correla- tions were suppressed by the inclusion of anti-mask data and with increased mask rank. As an application of this result, we explore how statistics-based alarming in nuclear security is impacted.

Fleenor, Matthew C↗
DOE OSTI2016

Non-uniform Neutron Source Approximation for Iterative Reconstruction of Coded Source Images

X-ray and neutron optics both lack ray focusing capabilities. An x-ray source can be made small and powerful enough to facilitate high-resolution imaging while providing adequate flux. This is not yet possible for neutrons. One remedy is to employ a computational imaging technique such as magnified coded source imaging. The greatest challenge associated with successful reconstruction of high-resolution images from such radiographs is to precisely model the flux distribution for complex non-uniform neutron sources. We have developed a framework based on Monte Carlo simulation and iterative reconstruction that facilitates high- resolution coded source neutron imaging. In this paper, we define a methodology to empirically measure and approximate the flux profile of a non-uniform neutron source, and we show how to incorporate the result within the forward model of an iterative reconstruction algorithm. We assess improvement in image quality by comparing reconstructions based respectively on the new empirical forward model and our previous analytic models.

Gregor, Jens↗
DOE OSTI2013

Coded Aperture Imaging for Fluorescent X-rays-Biomedical Applications

Employing a coded aperture pattern in front of a charge couple device pixilated detector (CCD) allows for imaging of fluorescent x-rays (6-25KeV) being emitted from samples irradiated with x-rays. Coded apertures encode the angular direction of x-rays and allow for a large Numerical Aperture x- ray imaging system. The algorithm to develop the self-supported coded aperture pattern of the Non Two Holes Touching (NTHT) pattern was developed. The algorithms to reconstruct the x-ray image from the encoded pattern recorded were developed by means of modeling and confirmed by experiments. Samples were irradiated by monochromatic synchrotron x-ray radiation, and fluorescent x-rays from several different test metal samples were imaged through the newly developed coded aperture imaging system. By choice of the exciting energy the different metals were speciated.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2013

Neutron imaging with coded sources: new challenges and the implementation of a simultaneous iterative reconstruction technique

The limitations in neutron flux and resolution (L/D) of current neutron imaging systems can be addressed with a Coded Source Imaging system with magnification (xCSI). More precisely, the multiple sources in an xCSI system can exceed the flux of a single pinhole system for several orders of magnitude, while maintaining a higher L/D with the small sources. Moreover, designing for an xCSI system reduces noise from neutron scattering, because the object is placed away from the detector to achieve magnification. However, xCSI systems are adversely affected by correlated noise such as non-uniform illumination of the neutron source, incorrect sampling of the coded radiograph, misalignment of the coded masks, mask transparency, and the imperfection of the system Point Spread Function (PSF). We argue that a model-based reconstruction algorithm can overcome these problems and describe the implementation of a Simultaneous Iterative Reconstruction Technique algorithm for coded sources. Design pitfalls that preclude a satisfactory reconstruction are documented.

Santos-Villalobos, Hector J↗
DOE OSTI2013

A Deployable Fast-Neutron Coded-Aperture Imager for Quantifying Nuclear Material

This brief report describes a newly constructed fast-neutron coded-aperture imager intended for performing quantitative measurements of plutonium holdup at fuel cycle facilities. The present report was prepared in fulfillment of milestone M4FT-13OR0402053, “Construct Imager,” of Fuel Cycle R&D Material Protection, Accounting, and Control Technology (MPACT) work package FT-13OR040205, “Fast-Neutron Imaging to Quantify Nuclear Materials - ORNL.” The first measurements taken with the imager will be reported later this year. For quantifying plutonium holdup, fast-neutron imaging is an appealing mode of measurement in scenarios where contact measurements with non-imaging detectors may be impractical or their results ambiguous because of surrounding material or nearby sources. The use of fast neutrons (as opposed to the more numerous gamma rays) is appealing because of their ability to penetrate equipment and nuclear material that is opaque to gamma radiation. However, the ability of fast neutrons to penetrate material also leads to challenges in constructing a fast-neutron imager sufficiently compact to be amenable for use in a facility while remaining sufficiently sensitive to neutron emanations from plutonium or other actinides. Furthermore, while fast-neutron detection is commonly achieved via organic liquid scintillators, use of the imager in a production environment favors mechanically robust detectors that do not contain flammable liquid. In response to these challenges, Oak Ridge National Laboratory (ORNL) has built a fast-neutron imager that has a compact footprint and whose segmented neutron detectors are built from the first cast plate of the recently developed plastic scintillator with pulse shape discrimination properties developed by Lawrence Livermore National Laboratory and commercially available from Eljen Technologies as experimental scintillator EJ-299-34.

Hausladen, Paul↗
DOE OSTI2014

Coded aperture imaging for fluorescent x-rays

We employ a coded aperture pattern in front of a pixilated charge couple device detector to image fluorescent x-rays (6–25 KeV) from samples irradiated with synchrotron radiation. Coded apertures encode the angular direction of x-rays, and given a known source plane, allow for a large numerical aperture x-ray imaging system. The algorithm to develop and fabricate the free standing No-Two-Holes-Touching aperture pattern was developed. The algorithms to reconstruct the x-ray image from the recorded encoded pattern were developed by means of a ray tracing technique and confirmed by experiments on standard samples.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

The Deployable Fast-Neutron Coded-Aperture Imager: Demonstration of Locating One or More Sources in Three Dimensions

This brief report describes commissioning measurements performed using a newly constructed fast neutron coded-aperture imager intended for performing quantitative measurements of plutonium holdup at fuel cycle facilities. The present report was prepared in fulfillment of milestone M3FT-13OR0402054, “Imager commissioning and 3D source configuration measurements” of Fuel Cycle R&D Material Protection, Accounting, and Control Technology (MPACT) work package FT-13OR040205, “Fast Neutron Imaging to Quantify Nuclear Materials - ORNL.” In addition to representing the first measurements made with the new device, these measurements also demonstrate for the first time the ability to localize one or more neutron sources in three dimensions by combining imaging data from multiple measurements in which the imager was positioned at different locations. The development and use of fast-neutron imaging technology are motivated by a desire to locate and quantify plutonium holdup in scenarios where contact measurements with non-imaging detectors may be impractical or their results ambiguous because of surrounding material or nearby sources. Considering the goal of quantitative measurements, fast neutrons (as opposed to the more numerous gamma rays) are preferred in many situations because of their ability to penetrate equipment and nuclear material that are essentially opaque to gamma radiation. However, there are many challenges associated with constructing a practical imager for fast neutrons. For example, the ability of fast neutrons to penetrate material also leads to challenges in constructing a fast-neutron imager that is sufficiently compact to be suitable for use in a facility while remaining sufficiently sensitive to neutron emanations from plutonium or other actinides. Moreover, use of the imager in a production environment favors mechanically robust detectors that do not contain flammable liquid, unlike the organic liquid scintillators that are typically used to achieve fast-neutron detection. Last of all, a single-sided measurement geometry, as is typically used in imaging applications, necessitates accurate measurement of the location of a deposit of plutonium holdup in three dimensions in order to correctly infer the source strength. In response to these challenges, Oak Ridge National Laboratory (ORNL) has built a fast-neutron imager that has a compact footprint and whose segmented neutron detectors are built from the first cast plate of the recently developed plastic scintillator with pulse shape discrimination properties developed by Lawrence Livermore National Laboratory and commercially available from Eljen Technologies as experimental scintillator EJ-299-34. This report presents a description and preliminary analysis of mock holdup measurements intended to determine the three-dimensional location of one or more neutron sources placed in prototypical equipment from a set of imaging measurements that scanned the extent of the equipment.

Hausladen, Paul↗
DOE OSTI2025

Whole-scene, one-sided backscatter x-ray imaging with coded apertures

X-ray radiography can be an important diagnostic for emergency response, providing timely diagnostic information about a suspect object. However, there are situations where similar information would be better obtained with a one-sided imaging technique. X-ray backscatter imaging is a proven technology that could provide such information, but current implementations have drawbacks that render it unsuitable for emergency response. We are exploring the use of coded-aperture imaging to create one-sided images, targeting a key benefit: implementation requiring minimal additional resources, bypassing logistics issues. We present results demonstrating the feasibility of this approach.

Ziock, Klaus-Peter [ORNL]↗
DOE OSTI2016

Thermal Neutron Imaging Using A New Pad-Based Position Sensitive Neutron Detector

Thermal neutrons (with mean energy of 25 meV) have a scattering mean free path of about 20 m in air. Therefore it is feasible to find localized thermal neutron sources up to ~30 m standoff distance using thermal neutron imaging. Coded aperture thermal neutron imaging was developed in our laboratory in the nineties, using He-3 filled wire chambers. Recently a new generation of coded-aperture neutron imagers has been developed. In the new design the ionization chamber has anode and cathode planes, where the anode is composed of an array of individual pads. The charge is collected on each of the individual 5x5 mm2 anode pads, (48x48 in total, corresponding to 24x24 cm2 sensitive area) and read out by application specific integrated circuits (ASICs). The high sensitivity of the ASICs allows unity gain operation mode. The new design has several advantages for field deployable imaging applications, compared to the previous generation of wire-grid based neutron detectors. Among these are the rugged design, lighter weight and use of non-flammable stopping gas. For standoff localization of thermalized neutron sources a low resolution (11x11 pixel) coded aperture mask has been fabricated. Using the new larger area detector and the coarse resolution mask we performed several standoff experiments using moderated californium and plutonium sources at Idaho National Laboratory. In this paper we will report on the development and performance of the new pad-based neutron camera, and present long range coded-aperture images of various thermalized neutron sources.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Detailed Characterization of CZT Detector Response for Improved Coded-Aperture Imaging Performance

Gamma-ray imaging is a powerful method for locating and quantifying sources of radiation. The coded-aperture technique demonstrates superior angular resolution in comparison to other methods (e.g., Compton reconstruction). In this method, a mask constructed of highly attenuating material encodes the scene as a shadow pattern on a position-sensitive detector; this pattern can then be used to recreate the origin(s) of incident radiation. This is typically done through convolution of the mask and shadow patterns. Iterative methods which attempt to reconstruct the observed shadow pattern using a weighted combination of simulated patterns may also be employed. In either case, errors in event position reconstruction due to detector imperfections alter the shadow pattern and will therefore degrade system performance and may introduce imaging artifacts. These effects can be mitigated with a detailed understanding of such errors – allowing for the generation of representative simulations that include the errors and/or correction of raw imager data to remove the errors. We present a calibration process for a commercially available cadmium zinc telluride (CZT) gamma imager which provides a comprehensive characterization of the spatial and energy dependence of event reconstruction. By illuminating a mask featuring a regular grid of pinholes with a calibration source, the localized response of the detector can be measured with fine granularity. These local responses are combined to generate a full detector response map which can be used to distort simulations in a manner that is representative of the observed detector data. Details of the calibration procedure and an assessment of the impact of its end products on the performance of iterative imaging methods will be presented.

Ziock, Klaus-Peter↗