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Weber, Thomas

Publications and source records attributed to Weber, Thomas.

16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Modification of a Silicon Photomultiplier for Reduced High Temperature Dark Count Rate

In this work we present a novel method for improving the high-temperature performance of silicon photomultipliers (SiPMs) via focused ion beam (FIB) modification of individual microcells. The literature suggests that most of the dark count rate (DCR) in a SiPM is contributed by a small percentage (<5%) of microcells. By using a FIB to electrically deactivate this relatively small number of microcells, we believe we can greatly reduce the overall DCR of the SiPM at the expense of a small reduction in overall photodetection efficiency, thereby improving its high temperature performance. In this report we describe our methods for characterizing the SiPM to determine which individual microcells contribute the most to the DCR, preparing the SiPM for FIB, and modifying the SiPM using the FIB to deactivate the identified microcells.

42 ENGINEERING↗
DOE OSTI2021

Open Radiation Monitoring: Conceptual System Design

The Open Radiation Monitoring (ORM) Project seeks to develop and demonstrate a modular radiation detection architecture designed specifically for use in arms control treaty verification (ACTV) applications that will facilitate rapid development of trusted systems to meet the needs of potential future treaties. Development of trusted systems to support potential future treaties is a complex and costly endeavor that typically results in a purpose-built system designed to perform one specific task. The majority of prior trusted system development efforts have relied on the use of commercial embedded computers or microprocessors to control the system and process the acquired data. These processors are complex, making authentication and certification of measurement systems and collected data challenging and time consuming. We believe that a modular architecture can be used to reduce more complex systems to a series of single-purpose building blocks that could be used to implement a variety of detection modalities with shared functionalities. With proper design, the functionality of individual modules can be confirmed through simple input/output testing, thereby facilitating equipment inspection and in turn building trust in the equipment by all treaty parties. Furthermore, a modular architecture can be used to control data flow within the measurement system, reducing the risk of "hidden switches" and constraining the amount of sensitive information that could potentially be inadvertently leaked. This report documents a conceptual modular system architecture that is designed to facilitate inspection in an effort to reduce overall authentication and certification burden. As of publication, this architecture remains in a conceptual phase and additional funding is required to prove out the utility of a modular architecture and test the assumptions used to rationalize the design.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2021

Novel Quantum Dot Technology Shows Promise in Simplifying Vehicle and Structural Surface Inspections

A team of researchers from both the Air Force Institute and Technology and Los Alamos National Laboratory are developing a paint that contains a material called quantum dots which can optically measure deformation of a surface. Quantum dots are the same materials used in new QLED television displays; however, they can also be used for a multitude of sensing applications such as deformation. The researchers used a new method of applying an interfacial layer between the quantum dot paint and the surface under investigation to help adhesion in harsh environments. The primary motivation behind this research is to make both quality assurance and maintenance of aircraft easier for the warfighter. The researchers’ efforts started in 2019 and are continuing. The technology works by shining a light onto the surface of the paint and the dots will emit back a wavelength of light that relates to the amount of deformation the surface is going through. This has the promise to allow for real-time 2D surface measurements that is more affordable than other 2D surface measurement alternatives.

42 ENGINEERING↗
DOE OSTI2020

HVDC Surface Flashover in Compressed Air for Various Dielectrics

Here, this study measures the voltage at which flashover occurs in compressed air for a variety of dielectric materials and lengths in a uniform field for DC voltages up to 100 kV. Statistical time lag is recorded and characterized, displaying a roughly exponential dependence on breakdown voltage. Of the materials tested, acrylic is observed to be the most resistant to flashover. These data are intended to facilitate the design of compressed-air insulated high voltage systems as an alternative to SF 6 insulated systems.

42 ENGINEERING↗
DOE OSTI2019

Stochastic and coarse-grained two-dimensional modeling of directional particle movement

In this work, we study the evolution of interacting groups of pedestrians in two-dimensional geometries. We introduce a microscopic stochastic model that includes floor fields modeling the global flow of individual groups as well as local interaction rules. From this microscopic model we derive an analytically-tractable system of conservation laws that governs the evolution of the macroscopic pedestrian densities. Numerical simulations show good agreement between the system of conservation laws and the microscopic model, though the latter is slightly more diffusive. We conclude by deriving second-order corrections to the system of conservation laws.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Correlated local dipoles in PbTe

We present a combined single-crystal x-ray diffuse scattering and ab-initio molecular dynamics study of lead telluride, PbTe. Well-known for its thermoelectric and narrow-gap semiconducting properties, PbTe recently achieved further notoriety following the report of an unusual off-centering of the lead atoms, accompanied by a local symmetry breaking, on heating. This observation, which was named emphanisis, ignited considerable controversy regarding the details of the underlying local structure and the appropriate interpretation of the total scattering experiments. In this study, we identify an unusual correlated local dipole formation extending over several unit cells with an associated local reduction of the cubic symmetry in both our x-ray diffuse scattering measurements and our molecular dynamics simulations. Importantly, when averaged spatially or temporally, the most probable positions for the ions are at the centers of their coordination polyhedra. Our results therefore clarify the nature of the local symmetry breaking, and reveal the source of the earlier controversy regarding the existence or absence of off-centering. Finally, we provide an interpretation of the behavior in terms of coupled soft optical and acoustic modes, which is linked also to the high thermoelectric performance of PbTe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magneto Inertial Fusion Plasma Target Collaboration: CRADA Final Report

The Participant and Los Alamos National Laboratory (LANL) investigated possible paths for compression of plasma targets in Magneto Inertial Fusion (MIF) regimes. MIF involves the addition of a magnetic field to Inertial Fusion type plasma targets, potentially improving energy confinement. This technique could reduce the power, precision, and cost required to compress and heat plasma targets to fusion relevant conditions, leading to a lower cost path to a fusion energy source. MIF regimes are intermediate between magnetic fusion energy and inertial fusion energy approaches. LANL is pursuing the creation of a MIF compatible magnetized plasma target with long enough lifetime to compress it inside a solid cylindrical, flux-conserving shell. The Participant also requires a similar plasma target for use with a novel acoustic wave compression scheme.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

A beam hardening and dispersion correction for x-ray dark-field radiography

Purpose: X-ray dark-field imaging promises information on the small angle scattering properties even of large samples. However, the dark-field image is correlated with the object’s attenuation and phase-shift if a polychromatic x-ray spectrum is used. A method to remove part of these correlations is proposed. Methods: The experimental setup for image acquisition was modeled in a wave-field simulation to quantify the dark-field signals originating solely from a material’s attenuation and phase-shift. A calibration matrix was simulated for ICRU46 breast tissue. Using the simulated data, a dark-field image of a human mastectomy sample was corrected for the finger print of attenuation- and phase-image. Results: Comparing the simulated, attenuation-based dark-field values to a phantom measurement, a good agreement was found. Applying the proposed method to mammographic dark-field data, a reduction of the dark-field background and anatomical noise was achieved. The contrast between microcalcifications and their surrounding background was increased. Conclusions: The authors show that the influence of and dispersion can be quantified by simulation and, thus, measured image data can be corrected. The simulation allows to determine the corresponding dark-field artifacts for a wide range of setup parameters, like tube-voltage and filtration. The application of the proposed method to mammographic dark-field data shows an increase in contrast compared to the original image, which might simplify a further image-based diagnosis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Ephemerality of discrete methane vents in lake sediments

Methane is a potent greenhouse gas whose emission from sediments in inland waters and shallow oceans may both contribute to global warming and be exacerbated by it. The fraction of methane emitted by sediments that bypasses dissolution in the water column and reaches the atmosphere as bubbles depends on the mode and spatiotemporal characteristics of venting from the sediments. Earlier studies have concluded that hot spots—persistent, high-flux vents—dominate the regional ebullitive flux from submerged sediments. Here the spatial structure, persistence, and variability in the intensity of methane venting are analyzed using a high-resolution multibeam sonar record acquired at the bottom of a lake during multiple deployments over a 9 month period. We confirm that ebullition is strongly episodic, with distinct regimes of high flux and low flux largely controlled by changes in hydrostatic pressure. Our analysis shows that the spatial pattern of ebullition becomes homogeneous at the sonar's resolution over time scales of hours (for high-flux periods) or days (for low-flux periods), demonstrating that vents are ephemeral rather than persistent, and suggesting that long-term, lake-wide ebullition dynamics may be modeled without resolving the fine-scale spatial structure of venting.

54 ENVIRONMENTAL SCIENCES↗