The NNSS has been at the forefront of custom high-fidelity x-ray/gamma radiographic imaging solutions that serve our national security for over five decades. Our radiography team utilizes expertise in physics modeling and analysis, along with optical, mechanical, and electrical design, in close collaboration with our customers, to develop imaging methods and capabilities that go beyond their needs. Conceptual designs are developed through R&D efforts to provide solutions for the specific problem at hand. Field systems are designed and built in-house, then qualified utilizing a range of facilities across the National Security Enterprise. Radiographic imaging systems are deployed by our team in the most challenging environments. The NNSS has a strong math and programming team that provides novel on-site image analysis methods that extract crucial information from data returned in field tests.

Cygnus is a dual beam high-energy radiographic x-ray source. Ten years ago, three large zoom lenses were assembled to collect images from 200 mm x 200 mm square scintillators. The zoom capability allows zooming down to a 60 mm x 60 mm picture from the scintillator. Current radiographic imaging needs now require larger 270 mm x 270 mm square scintillators and the capability to use both 92 mm x 92 mm and 62 mm x 62 mm CCD cameras, and a new lens design to meet these needs. This zoom lens incorporates 11 elements and is designed to be telecentric. It images a scintillator emitting light peaking at 435 nm, so special glass types are required for the lens elements. Much larger elliptical pellicles are needed to deflect the scintillator light out of the x-ray path into the lens. The optical axis of the imaging system must be colinear with the x-ray axis. Two scintillators are positioned in each of two Cygnus x-ray axes, for a total of four scintillators and four lens systems. An optional configuration will be shown, enabling two lens systems imaging opposite sides of a single scintillator, for a total of four lenses and two scintillators. Although this configuration has advantages, it suffers from crosstalk. Care must be taken to analyze the anti-reflection coatings applied to all the elements in the imaging chain, including the CCD array and its vacuum window. The evolution of our Cygnus radiographic systems over the last two decades will be discussed.

Presentation to be presented during the first annual Prompt Radiation Detection and Imaging Workshop, hosted by the NNSS Dynamic Instruments Team, April 25–28, 2022, at NLV C-01 Auditorium and via Webex.

Presentation to be presented during the first annual Prompt Radiation Detection and Imaging Workshop, hosted by the NNSS Dynamic Instruments Team, April 25–28, 2022, at NLV C-01 Auditorium and via Webex.

science starting with the Manhattan Project has positioned us well to develop a contemporary materials strategy pushing the frontiers of controlled functionality - the design and tailoring of a material for the unique demands of a specific application. Controlled functionality requires improvement in understanding of the structure and properties of materials in order to synthesize and process materials with unique characteristics. In the nuclear weapons program today, improving data and models to increase confidence in the stockpile can take years from concept to new knowledge. Our goal with MaRIE is to accelerate this process by enhancing predictive capability - the ability to compute a priori the observables of an experiment or test and pertinent confidence intervals using verified and validated simulation tools. It is a science-based approach that includes the use of advanced experimental tools, theoretical models, and multi-physics codes, simultaneously dealing with multiple aspects of physical operation of a system that are needed to develop an increasingly mature predictive capability. This same approach is needed to accelerate improvements to other systems such as nuclear reactors. MaRIE will be valuable to many national security science challenges. Our first issue of Vistas focused on our current national user facilities (the Los Alamos Neutron Science Center [LANSCE], the National High Magnetic Field Laboratory-Pulsed Field Facility, and the Center for Integrated Nanotechnologies) and the vitality they bring to our Laboratory. These facilities are a magnet for students, postdoctoral researchers, and staff members from all over the world. This, in turn, allows us to continue to develop and maintain our strong staff across the relevant disciplines and conduct world-class discovery science. The second issue of Vistas was devoted entirely to the Laboratory's materials strategy - one of the three strategic science thrusts for the Laboratory. This strategy has helped focus our thinking for MaRIE. We believe there is a bright future in cutting-edge experimental materials research, and that a 21st-century facility with unique capability is necessary to fulfill this goal. The Laboratory has spent the last several years defining MaRIE, and this issue of Vistas presents our current vision of that facility. MaRIE will leverage LANSCE and our other user facilities, as well as our internal and external materials community for decades to come, giving Los Alamos a unique competitive advantage, advancing materials science for the Laboratory's missions and attracting and recruiting scientists of international stature. MaRIE will give the international materials research community a suite of tools capable of meeting a broad range of outstanding grand challenges.

Framing cameras provide a discrete series of images over a short period of time in a manner that mimics a high-speed movie camera but with individual shutter times that must be extremely short in order to capture freeze-frame images of rapidly evolving phenomena such as high-explosive shock-driven ejecta, dynamic compression of metals, and high-velocity fluid flow. The Nevada National Security Site has designed and fielded a new, large-area, gated framing camera called Kraken. The camera design emphasized manufacturability and flexibility by improving imager yield and creating a camera architecture to shorten design cycles. Design strategies and field data are presented.

coping strategy (FLEX), enhancements to plant components and systems, and the incorporation of augmented or new passive cooling systems, as well as improved fuel cycle efficiency. The objective of the ERP research effort is to use the RISA methods and toolkit in industry applications, including methods development and early demonstration of technologies, in order to enhance existing reactors’ safety features (both active and passive) and to substantially reduce operating costs through risk-informed approaches to plant design modifications to the plant and their characterization. One main focus of the FY 2020 efforts documented in this report was to extend the analyses conducted in FYs 2018 and 2019 for a pressurized water reactor (PWR) to a boiling water reactor (BWR). The same analysis process, risk analysis approaches, and analysis tools as in the previous work for PWR were used for a generic BWR with near-term ATF cladding (i.e., Iron-Chromium-Aluminum [FeCrAl] cladding and Chromium [Cr]-coated cladding) designs under the postulated station blackout (SBO) and medium loss-of-coolant (MLOCA) accident scenarios. In addition, a FLEX model was developed and incorporated into a generic BWR probabilistic risk assessment (PRA) model using the INL-developed software tool, Systems Analysis Programs for Hands-on Integrated Reliability Evaluations (SAPHIRE), to assess the risk impact from FLEX. The other main focus of the FY 2020 efforts was to advance analysis methods, including developing dynamic approach for FLEX human reliability analysis (HRA) using the INL-developed software tool, Event Modeling Risk Assessment using Linked Diagrams (EMRALD), as well as developing a multicriterion benefit evaluation (MCBE) method for evaluating costs and benefits of safety enhancements in nuclear power plants (NPPs). As a case study, the MCBE method was applied to evaluate the costs and benefits brought by FLEX implementation.

Interrogating ejecta particles launched from target materials that are undergoing dynamic shock can be done with both xray imaging and visible shadowgraph imaging. Our dynamic testing must be done inside a containment vessel with limited access ports available. We designed an imaging system to relay both types of imaging systems through a single port using the same optical relay and then splitting the images onto three separate high-speed imaging cameras outside the containment vessel. X-ray imaging provides ejecta density measurements. Shadowgraph imaging that is done at two wavelengths (blue and red) constrains ejecta particle size distributions and provides areal density measurements of the ejecta cloud. The ejecta particles are positioned 225 mm before the x-ray scintillators; this arrangement permits a folded mirror system to allow the shadowgraph data to bypass the x-ray scintillators. This configuration results in spatial separations between the intermediate image planes of the x-ray and shadowgraph images along the optical axis. At the position of the x-ray intermediate image plane, mirrors are positioned such that the shadowgraph images are kicked out and their images are sent on to different cameras. Positioning of the large doublet relay lenses keeps shrapnel from impacting the vessel containment windows.

This work describes and shows data from a prototype instrument designed to sample transitory gamma rays resulting from stockpile stewardship testing. The required instrumentation needs to be large, sensitive, low cost, and have the ability to measure pulse widths as narrow as 5 ns (or less). The natural material for an instrument to meet these criteria is an organic scintillator. In order to cover a large area and reduce the overall cost of the detection system (material and electronics), one approach would be large pixel elements to cover an array of a few square meters. Unfortunately, this approach will not provide the accuracy required for these experiments as large volume scintillation detectors broaden the intrinsic full-width at half maximum (FWHM) of the scintillation light pulse due to delays introduced by internal reflections within the scintillator volume. We devised an approach to mitigate these broadening effects from large volume detectors, while remaining at a low cost. Our detectors consist of a bundle of extruded plastic scintillation bars, readout by wavelength shifting fibers that pipe the scintillation light to a fast light readout device. In this paper we describe the detector unit and assembly procedure, the fast photomultiplier tube (PMT) and readout electronics, as well as data from the laboratory with a radioactive source and cosmic-ray muons. Additionally, we show results from a detector unit tested at the NRL Mercury pulsed power facility. The concluding section discusses the path forward for this instrument and possible improvements for a field-deployable system.

High-energy X-ray radiographic image restoration is performed using a simulated radiation point spread function and an experimentally derived optical point spread function. It is shown that a robust method for removal of thick monolithic scintillator blur can be determined through independent examination of the blur components. We show that the scintillator blur for a 20 MeV end-point X-ray beam and 20 mm thick LYSO scintillator contributes significantly to the system blur. It is also shown that the optical scatter in the monolithic crystal degrades the low-frequency response of the system. The use of a simulated point spread function for image restoration using deconvolution provides a simple method for image restoration, thereby enhancing feature identification and areal density reconstruction.

The Gamma Array Simulation Toolkit (GAST) is a multi-physics software stack comprised of Geant4, MATLAB, and experimentally measured photomultiplier tube (PMT) impulse response waveforms that is used to model and inform the end-to-end performance of radiation detector systems. In order to validate the ability of GAST to predict the impulse response of a modeled detector configuration operated in current mode, experimental measurements using the Nevada National Security Site Transformational Diagnostics and Imaging 2 MeV endpoint energy electron linear accelerator (linac) with a tungsten target were performed. Seven different detector configurations consisting of unique combinations of scintillator material, size, reflectivity conditions, presence or absence of light guide, and PMT were evaluated. The resultant impulse response of each detector configuration was recorded and compared to a GAST simulation that emulated the respective linac experiment conditions. The comparison of the experimental and simulated detector impulse responses indicated that GAST can reliably predict detector impulse responses.

Experimental measurements were performed to characterize the impulse response of seven different gamma ray detector prototypes being considered to be fielded as a current mode diagnostic for neutron-diagnosed subcritical experiments at the Nevada National Security Site (NNSS). For such experiments, the impulse response of the fielded detector is required to have a full-width half-maximum (FWHM) of approximately 5 ns or less and a low amplitude tail. Each of the detector prototypes evaluated in this work were selected based on the potential to meet this performance requirement. An impulse of bremsstrahlung x-rays created from 2 MeV electrons from the NNSS's Transformational Diagnostics and Imaging, Los Alamos, linear accelerator was measured with each detector. The measured impulse response was evaluated for each detector configuration. A comparison of these impulse responses revealed a relationship between fast timing performance and scintillator material, geometry, surface reflectivity conditions, and photomultiplier tube (PMT) selection. The detector configuration yielding an impulse response with the shortest FWHM of 3.82 +/- 0.11 ns and possessing a low amplitude tail was a 5-inch (12.7-cm) diameter, 5-inch (12.7-cm) height cylindrical EJ-399-17-VI liquid scintillator in a black-painted housing coupled to an Adit D798B 5-inch (12.7-cm) PMT by means of a 0.079-inch (0.2-cm) EJ-560 optical coupling pad.

A comprehensive comparison of the dominant sources of radiation-induced blur for radiographic imaging system performance is made. End-point energies of 6, 10, 15, and 20 MeV bremsstrahlung photon radiation produced at the Los Alamos National Laboratory Microtron facility were used to examine the performance of large-panel cerium-doped lutetium yttrium silicon oxide (LYSO:Ce) scintillators 3, 5 and 10 mm thick. The system resolution was measured and compared between the various end-point energies and scintillator thicknesses. Contrary to expectations, it is found that there was only a minor dependence of system resolution on scintillator thickness or beam end-point energy. This indicates that increased scintillator thickness does not have a dramatic effect on system performance. The data are then compared to Geant4 simulations to assess contributions to the system performance through the examination of modulation transfer functions. It was determined that the low-frequency response of the system is dominated by the radiation-induced signal, while the higher-frequency response of the system is dominated by the optical imaging of the scintillation emission.

This milestone report describes development of the Digital Time-Resolved Spot Diagnostic (D-TRSD) into a functioning diagnostic that has been proven in the laboratory. Laboratory tests complete the MRT 6744 exit criteria with the recording and analysis of a spot size measurement for two consecutive pulses on a two-pulse source. Additional channels will be added in the near future to provide an 84-channel measurement capability. The new modular design is more portable than the previous generations and will be much easier to set up at radiographic facilities across the complex.

Often only a single physical process or component is investigated in the simulation of radiation detector systems. The results are then considered to be representative of what is expected in the correlating physical experiment. Although singular assessments may serve as a good estimate, the overall performance of a radiation detector system depends on several physical processes and the performance of all components within the system. Our Geant4-based multiphysics simulation toolkit couples radiation transport with optical photon processes, providing simulations of radiation detector systems components from the scintillator through the photocathode of the photodetector. Work to incorporate the backend detector components, including the complete photodetector and subsequent electronics (e.g., amplifiers, digitizers), is underway. Geant4 is used to model the radiation transport and optical photon processes that occur in the front-end detector system components when exposed to a chosen source. These components include the scintillator, detector housing, optical coupling to the photodetector, and photocathode of the photodetector. Characteristics of several detector systems that have been studied include time response; pulse height spectra; number of photoelectrons per MeV; detector efficiency versus incident quanta energy; and effects on detector response due to change in geometries, materials, and reflectivity. Comparison of these characteristics by means of this toolkit enables the selection of the optimal individual components; thus, it is possible to specify the radiation detector system best suited to meet the requirements of any physical experiment.

The digital time-resolved spot diagnostic (D-TRSD) is intended to be a fast-response, time-dependent beam diagnostic for measuring the spot size emitted from radiographic x-ray sources. It will measure spot sizes from submillimeters up to several millimeters for photon energies in the range of 150 keV to 20 MeV with doses as low as 0.03 rad up to 500 rad. The D-TRSD performs fast data acquisition as radiographic x-ray sources typically produce pulses in the tens of nanosecond ranges. The system will be optimized to capture multiple individual pulses in time within the same data record. The data collected will be used to support beam tuning and source optimization with on-the-fly evaluation of radiographic source performance. The diagnostic is based on penumbral imaging techniques. A scintillating fiber array of parallel aligned fibers is positioned in the beam path with a high-Z rolled edge inserted between the source and the array, thereby creating the penumbral x-ray signal that is captured by the D-TRSD system. The light from the scintillation conversion is recorded by individual avalanche photodiode detectors integrated into custom digitizer electronics. The penumbra is used to calculate the spot of the beam on the axis orthogonal to the fiber array based on the magnification from the rolled edge, the resolution of the spaced fibers, and the rotation of the array normal to the beam path. Many arrays can be used to capture additional spot widths about different rotations. The D-TRSD system is modular, software-driven, and easier to use than legacy TRSD systems.