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Air Force Institute of Technology

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Full-Text Articles in Nuclear Engineering

Validation Of Unstructured Mesh Capability For Modeling Variable Density Objects Using Mcnp®, William K. Backman Mar 2023

Validation Of Unstructured Mesh Capability For Modeling Variable Density Objects Using Mcnp®, William K. Backman

Theses and Dissertations

MCNP® is a radiation transport code with the capability to define geometries using unstructured meshes. While this geometry type was intended to help model complex geometries, it also has the capability of being used to model objects with variable density. This can be done by assigning varying density values to different elements in a mesh. This capability has not been well explored, though it could be beneficial for several applications within the nuclear engineering community.


A Method For Monte Carlo Neutral Particle Radiation Transport In A Variable Density Atmosphere, Aidan B. Edens Mar 2023

A Method For Monte Carlo Neutral Particle Radiation Transport In A Variable Density Atmosphere, Aidan B. Edens

Theses and Dissertations

This study focuses on accurately simulating the transport of radiation in the atmosphere to better understand the effects of nuclear weapons. The variable nature of the atmosphere poses a challenge in accurately simulating the prompt radiation following a nuclear explosion. To address this challenge, the Mass Integral Scaling technique is integrated with the Monte Carlo method to perform calculations in a variable density atmosphere. In addition to previous free-field estimates, this work also enables the simulation of transport calculations with other media, such as clouds. Results of neutron and photon fluence have been verified against the standard version of MCNP …


Exploring Variations In Fast Curing Plastic Scintillator Formulations: Optimizing Tpo And Evaluating The Effects Of High-Z Loading And Novel Waveshifters, Andrew K. Nesbitt Mar 2023

Exploring Variations In Fast Curing Plastic Scintillator Formulations: Optimizing Tpo And Evaluating The Effects Of High-Z Loading And Novel Waveshifters, Andrew K. Nesbitt

Theses and Dissertations

Organic plastic scintillators are widely used due to their relative low cost, physical robustness, and fast timing properties, but typically provide lower light yields and photon sensitivity compared to other alternatives. Photocuring novel plastics offers a viable method for producing fast curing plastic scintillators. The current formulations include an acrylic polymer base and utilize diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as the photo-initiator for polymerization; however at higher concentrations of TPO may adversely affect scintillator light output. The present research refined the optimal TPO concentrations that fully cure these acrylic-base scintillators and maximize light production to 0.4-0.5% by weight. Additionally, this …


Automated Additive Layering Of Vat Polymerized Plastic Organic Scintillators, Chandler J. Moore Mar 2023

Automated Additive Layering Of Vat Polymerized Plastic Organic Scintillators, Chandler J. Moore

Theses and Dissertations

The current technology for fast neutron detection imaging is limited in achieving the required high spatial resolution, strong neutron discrimination, and practical time of manufacturing. Traditional fabrication methods require days of thermal polymerization and hundreds of man-hours to produce average resolution pixelated scintillator arrays. The present work helps to eliminate this limitation by developing an additive manufacturing technique to construct such detectors for use in in dual particle imaging applications. In this work, fast-, light-curing resins are used in a prototype automated assembly machine, capable of layering of individual light-cured resin layers and optical segmentation with a self-bonded specular reflector, …


Angle Resolved Photoelectron Spectroscopy Study Of Germanium Tin: Experimentally Determined Electronic Band Gap And Surface Analysis, Jeremy M. Hunter Mar 2023

Angle Resolved Photoelectron Spectroscopy Study Of Germanium Tin: Experimentally Determined Electronic Band Gap And Surface Analysis, Jeremy M. Hunter

Theses and Dissertations

The germanium tin band gap is responsive to wavelengths in the mid to near infrared spectrum; this shows promise in meeting the detection demands of the next generation infrared detectors. Recent developments in germanium tin (GeSn) alloy growth techniques have peaked the scientific community’s interest in GeSn based optoelectrical and detection devices. Detection materials made entirely of group IV elements are compatible with complementary metal-oxide semiconductor manufacturing techniques. Understanding the surface chemistry of this alloy is fundamental for solid state device design and must be analyzed to optimize device performance. Studies have shown that with the addition of tin, the …


Fabrication And Testing Of A Novel Layered Metascintillator For Neutron And Gamma Discrimination, Evan W. Threlkeld Mar 2023

Fabrication And Testing Of A Novel Layered Metascintillator For Neutron And Gamma Discrimination, Evan W. Threlkeld

Theses and Dissertations

By leveraging new developments in fast-curing of plastic scintillators, it is possible to fabricate multi-material plastic scintillators, or metascintillators, which offer improved and/or novel capabilities for radiation detection. This document proposes one geometry of metascintillator that uses layers of green and blue scintillating material to discriminate neutron/gamma radiation, details the devices necessary to fabricate it, and analyzes the metascintillator’s response to radiation. A model of the metascintillator using Geant4 and Python suggested that spectral-based neutron/gamma event discrimination is possible with 63% of gamma events and only 1% of neutron events being multi-color. Fabrication of a 500 µm per layer metascintillator …


Fast Engineering Model For Defect Production In Magnesium Oxide, Henry R. Little Mar 2023

Fast Engineering Model For Defect Production In Magnesium Oxide, Henry R. Little

Theses and Dissertations

Defect production from irradiation of materials with thicknesses much less than the mean free path for neutron interaction is explored. A model is developed using the Monte Carlo N-Particle transport code from Los Alamos National Laboratory, experimental data from irradiations at the Oak Ridge High Flux Isotope Reactor, defect production theory, and atomistic simulation results to predict the total number of F-centers resulting from neutron irradiation of a MgO rod. This model accurately predicts the concentration of atomic defects under conditions closely matching experiments at long timescales, for large geometries, and requiring only 6.9 minutes on a single CPU. Results …


Simulation Of Neutron Generation From Laser-Driven Fusion In A Liquid D2o Sheet Using Novel Warpx Module, Colton R. Stoner Mar 2023

Simulation Of Neutron Generation From Laser-Driven Fusion In A Liquid D2o Sheet Using Novel Warpx Module, Colton R. Stoner

Theses and Dissertations

Using WarpX’s new nuclear fusion module, this work attempts to model an experimental system at the ELL at the AFIT with WarpX and draw conclusions about fusion products from resulting simulations. Recently, a table-top, high repetition rate, mixed radiation source was demonstrated at the ELL employing a HIL to fuse the deuterium nuclei present in a unique liquid target of heavy water. Analysis of the simulations predicted an isotropic output of neutrons from deuterium-deuterium fusion. These simulated neutrons were created in tens of femtoseconds from dense bodies of deuterons that were perturbed by the laser. However, it was found that …


Assessment Of Emergency Cooling Requirement For Nuclear Reactor Loss-Of-Coolant Accidents, Michael T. Lindsay Mar 2023

Assessment Of Emergency Cooling Requirement For Nuclear Reactor Loss-Of-Coolant Accidents, Michael T. Lindsay

Theses and Dissertations

The 2022 Russia-Ukraine War marks the first time in modern history of conventional military forces targeting and seizing control of an operational nuclear power plant. Power supply and operational cooling systems are critical to avert reactor loss-of-coolant accidents (LOCA) in the event of emergency shutdown, or SCRAM. A wartime non-design based reactor accident causing loss of reactor power and coolant supply would require an emergency heat exchange via coolant to mitigate reactor core heat. At present, the military does not have a well-defined model which characterizes this requirement for operational planning should such an event occur. SCALE 6.2.4 is used …


Pulsed Power Neutron Production With Deuterated Polymer Accelerator Targets, Anthony O. Hagey Mar 2023

Pulsed Power Neutron Production With Deuterated Polymer Accelerator Targets, Anthony O. Hagey

Theses and Dissertations

This document presents an investigation of the effect of deuterated polyethylene accelerator targets on the neutron fluence from a local mass injection dense plasma focus driven by the United States Naval Research Laboratory’s Hawk pulsed-power generator. After successful production of thin targets, the acquisition of thicker targets, and testing inside Hawk, it was found that the presence of a deuterated polyethylene target increased the neutron fluence. Results suggested that fluence can significantly increase with the presence of a deuterated target vs a nondeuterated target. Additive manufacturing printing was used as a production method in order to determine if deuterated accelerator …


Enabling Rapid Chemical Analysis Of Plutonium Alloys Via Machine Learning-Enhanced Atomic Spectroscopy Techniques, Ashwin P. Rao Sep 2022

Enabling Rapid Chemical Analysis Of Plutonium Alloys Via Machine Learning-Enhanced Atomic Spectroscopy Techniques, Ashwin P. Rao

Theses and Dissertations

Analytical atomic spectroscopy methods have the potential to provide solutions for rapid, high fidelity chemical analysis of plutonium alloys. Implementing these methods with advanced analytical techniques can help reduce the chemical analysis time needed for plutonium pit production, directly enabling the 80 pit-per-year by 2030 manufacturing goal outlined in the 2018 Nuclear Posture Review. Two commercial, handheld elemental analyzers were validated for potential in situ analysis of Pu. A handheld XRF device was able to detect gallium in a Pu surrogate matrix with a detection limit of 0.002 wt% and a mean error of 8%. A handheld LIBS device was …


Neutron Spectral Effect On Microelectronic Performance Response, Wade Kloppenburg Mar 2022

Neutron Spectral Effect On Microelectronic Performance Response, Wade Kloppenburg

Theses and Dissertations

Response of 2N2222 bipolar junction transistors to neutrons from a pulsed thermonuclear or pulsed fission source are researched. Measurements used for comparing performance included the base-collector junction current-voltage and capacitance-voltage characteristics and device gain degradation. Little change was detected in steady-state operation of the base-collector junction, but evidence in the dynamic and capacitance measurements establish effects based on environment. Experimental results are compared to literature results and parameters are explored using a device model simulation code.


Feasibility Of Fireball Trail Detection Using Ground-Based Gps Receivers, Ian R. Moffett Mar 2022

Feasibility Of Fireball Trail Detection Using Ground-Based Gps Receivers, Ian R. Moffett

Theses and Dissertations

The feasibility of using GPS data to detect fireballs is analyzed by first modeling the fireball’s trail diffusion and plasma chemistry to get a resulting ion density profile of the trail over time. The signal perturbation caused by the fireball trail is simulated for a ground receiver using an analytic solution for diffraction from a Gaussian lens. Five cases were modeled with varying initial peak ion densities and altitudes taken from fireball and reentry vehicle data. This paper shows that it is feasible to detect a fireball trail using GPS if the fireball has a sufficiently high initial ion density, …


Optimization Of A Multi-Layered Target For A Pulsed Power Neutron Source, Zachary D. Bretz Mar 2022

Optimization Of A Multi-Layered Target For A Pulsed Power Neutron Source, Zachary D. Bretz

Theses and Dissertations

The ability to create neutron environments is critical fora wide variety of applications including national security, materials science, and medical research. It is also helpful in medical, material, and other research. The U.S. Naval Research Laboratory (NRL), Washington, DC, is interested in leveraging their pulsed-power facilities to produce an in-house, relatively inexpensive neutron source. NRL’s facilities produce 2 MeV (from Gamble II) and 5 MeV (from Mercury) protons and deuterons. This research explored combinations of target materials to produce the most neutrons in the forward direction. Models of the reactions involved were first validated against literature experiments, then target designs …


Verficiation And Validation Of Unstructured Meshing Capabilities In Mcnp6, Micah C. Jeroutek Mar 2022

Verficiation And Validation Of Unstructured Meshing Capabilities In Mcnp6, Micah C. Jeroutek

Theses and Dissertations

Discrepancies were found between the legacy CSGs and the new UMs with the latter's introduction in MCNP6. As such, V&V of UMs in MCNP must be conducted to assist in their further development and increase user confidence in them. Currently, the MCNP test suite is lacking in UM benchmarks, and of the few that are present, their range in problem type is limited. To address these issues, two preliminary test cases covering new applications of UMs were developed for future inclusion in the test suite. The first was for the Athena-I experiment which involved the study of electronic devices' responses …


Capability Development For Advanced (N,X) Nuclear Data Measurements, Brian G. Frandsen Mar 2022

Capability Development For Advanced (N,X) Nuclear Data Measurements, Brian G. Frandsen

Theses and Dissertations

Nuclear reaction data are the heart of radiation transport calculations, models, and simulations. Unique approaches are required to improve the measurement capability for many reactions where data are inaccurate or do not exist. First, the newly developed Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) provides the ability to measure neutron inelastic scattering cross sections on different targets. An initial experiment measuring the 16O(n,n’𝛾) reaction calculated the count rate from the second excited state using the full energy and escape peaks. Second, a set of photocurable scintillator resin formulations capable of neutron-gamma discrimination were developed to support light-based …


Modeling Gadolinium Self Powered Neutron Detectors In A Transient Reactor, Alexander L. Q. Spring Mar 2022

Modeling Gadolinium Self Powered Neutron Detectors In A Transient Reactor, Alexander L. Q. Spring

Theses and Dissertations

Contributions to the electron current from the three components of a gadolinium SPND, emitter, insulator, and sheath, are identified, characterized, and quantified to provide information on how the SPND interacts within the transient neutron and photon flux of the TREAT to create a measurable current. These contributions are measured by defining the SPND interactions as a dose response function used within a Monte Carlo simulation of a TREAT experiment. The data obtained from the Monte Carlo simulations are then used to compare against two analytic models, developed by Jaschik and Warren, as well as the experimental results. It was found …


Deep Learning Approach To Multi-Phenomenological Nuclear Fuel Cycle Signals For Nonproliferation Applications, Preston J. Dicks Mar 2022

Deep Learning Approach To Multi-Phenomenological Nuclear Fuel Cycle Signals For Nonproliferation Applications, Preston J. Dicks

Theses and Dissertations

In order to reduce the time required for data analysis and decision-making relevant to nuclear proliferation detection, Artificial Intelligence (AI) techniques are applied to multi-phenomenological signals emitted from nuclear fuel cycle facilities to identify non-human readable characteristic signatures of operations for use in detecting proliferation activities. Seismic and magnetic emanations were collected in the vicinity of the High Flux Isotope Reactor (HFIR) and the McClellan Nuclear Research Center (MNRC). A novel bi-phenomenology DL network is designed to test the viability of transfer learning between nuclear reactor facilities. It is found that the network produces an 84.1% accuracy (99.4% without transient …


Analysis Of Microscopic Carbon Fiber Fragments, Zachary R. Scott Mar 2022

Analysis Of Microscopic Carbon Fiber Fragments, Zachary R. Scott

Theses and Dissertations

Carbon Fiber (CF) has different tensile strengths and transverse moduli depending on how they are fabricated. Some CF is export controlled as it can be used for weapons, spacecraft, or gas centrifuges for enriching nuclear fuel. This research project explored a new way to prepare micron sized single CF threads to measure their transverse modulus and compare the moduli of non-export controlled CF to that of an export controlled CF. Five total polyacrylonitrile (PAN) fibers were used in this project, one of which was an export controlled fiber.


Neutron Energy Tuning Assemblies For Nuclear Weapon Environment Applications At The National Ignition Facility, Nicholas J. Quartemont Sep 2021

Neutron Energy Tuning Assemblies For Nuclear Weapon Environment Applications At The National Ignition Facility, Nicholas J. Quartemont

Theses and Dissertations

An energy tuning assembly was developed to spectrally shape the National Ignition Facility deuterium-tritium fusion neutron source to a notional thermonuclear and prompt fission neutron spectrum to fulfill neutron source capability gaps. The experimental neutron environment was characterized with activation dosimetry, neutronics and covariance models, and unfolded to determine the as-fielded neutron spectrum. The first energy tuning assembly was demonstrated to create synthetic spectrally accurate post-detonation fission products, enhancing U.S. technical nuclear forensics capabilities. ATHENA, a second-generation energy tuning assembly, was also optimized to meet similar objectives, but the new platform neutron fluence efficiency was increased by a factor of …


Verification And Validation Of Radiation Protection Factors From Monte Carlo Simulations, William J. Erwin Sep 2021

Verification And Validation Of Radiation Protection Factors From Monte Carlo Simulations, William J. Erwin

Theses and Dissertations

This dissertation describes the verification and validation of methods for producing radiation protection factors (RPFs) using experiments and Monte Carlo N-Particle 6 (MCNP6) simulations. RPF validation of a steel enclosure using a plutonium-beryllium source produced a validated RPF with statistically significant agreement between neutron MCNP6 models and experiments and a gamma protection factor (GPF) with statistically significant agreement to the measured GPF. Efforts to validate more complex enclosures using the Fast Burst Reactor (FBR) yielded the first-ever direct measurements of this reactor’s prompt gamma emission spectrum and revealed irreconcilable differences between the FBR facility-provided source spectrum and spectrometer measurements, resulting …


Lithium Compound Characterization Via Laser Induced Breakdown Spectroscopy And Raman Spectroscopy, James T. Stofel Mar 2021

Lithium Compound Characterization Via Laser Induced Breakdown Spectroscopy And Raman Spectroscopy, James T. Stofel

Theses and Dissertations

Industries such as lithium-ion battery producers and the nuclear industry community seek to produce and store lithium in pure chemical forms. However, these lithium compounds are reactive with the atmosphere and quickly degrade into less desirable forms. Therefore, industry desires a fast and effective quality control approach to quantify the ingrowth of these secondary lithium chemical forms. This research presents a novel approach using Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy in tandem to enhance lithium compound characterization beyond what is achieved by either technique alone. The resulting spectral data are aggregated using data fusion and analyzed using chemometrics for …


Space To High-Altitude Region Adjoint Neutron Transport, Zachary W. Lamere Mar 2021

Space To High-Altitude Region Adjoint Neutron Transport, Zachary W. Lamere

Theses and Dissertations

The goal of this work was to use the adjoint transport equation to characterize the energy spectrum of a point neutron source using the time-energy fluence at the satellite. The adjoint transport was solved via Monte Carlo methods in the new program called Space to Air High-Altitude Region Adjoint (SAHARA). A new adjoint source event estimator was developed to improve the computational efficiency. This work explores SAHARA’s performance using mono-energetic and continuous sources. In general, the identified source spectra were noticeably shifted towards lower energies, but were able to capture the source spectrum shapes. Lastly, SAHARA was applied to the …


Characterization And Analysis Of Bomarc Accident Debris, Aaron J. Heffelfinger Mar 2021

Characterization And Analysis Of Bomarc Accident Debris, Aaron J. Heffelfinger

Theses and Dissertations

Accidents involving nuclear weapons, such as the Boeing Michigan Aeronautical Research Center (BOMARC) accident in 1960, always pose a significant risk of allowing particles composed of nuclear materials to enter the environment. These particles often differ in characteristics and can be of greatly varying sizes. Gamma ray analysis was conducted on the soil sample and radioisotopes within the sample were identified. Two non-destructive methods for locating actinide bearing particles within the sample were testing, resulting in 70 actinide bearing particles ranging from 1-34 microns being identified. These 70 particles underwent both morphological and elemental characterization, indicating uranium and other elements.


Application Of Artificial Neural Networks To Elemental Assay Data For Nuclear Forensics Analysis, Jason G. Seik Mar 2021

Application Of Artificial Neural Networks To Elemental Assay Data For Nuclear Forensics Analysis, Jason G. Seik

Theses and Dissertations

There is a need to quickly and accurately determine the likely physical origins of a collected sample for nuclear treaty verification purposes. The objective of this research is to prove there is a means to relate different samples (Q-values) to one another using a 'same versus not-same' artificial neural network called a Siamese network. This would provide the capability of comparing an unknown sample to a database of samples with known physical origins. Using moment transformations on current data has shown to increase the prediction capabilities of a Siamese network, and using a triplet loss function in connection with the …


Characterization Of The Spatial Distribution And Evolution Of Cerium And Calcium In Laser Produced Plasma, Michael G. Rynders Mar 2021

Characterization Of The Spatial Distribution And Evolution Of Cerium And Calcium In Laser Produced Plasma, Michael G. Rynders

Theses and Dissertations

Understanding plasma plumes and the distribution of plasma species microseconds after their formation has a variety of applications in fields such as hypersonics, explosion and combustion dynamics, and nuclear fireball chemistry. In this work, Laser Induced Breakdown Spectroscopy (LIBS) using double pulses of 532 nm light were used to analyze samples of cerium in atmospheres of air, vacuum, and argon. Cerium was used in this experiment to serve as a plutonium surrogate. CeO2 powder was pressed with CaO at 90-10 ratio to produce calcium doped pellets for use as sputtering targets. Inclusion of calcium impurities allowed the identification of …


Analysis Of The Correlation Between Re Filament Surface Features And Tims Performance, Christopher J. Mihal Mar 2020

Analysis Of The Correlation Between Re Filament Surface Features And Tims Performance, Christopher J. Mihal

Theses and Dissertations

Thermal Ionization Mass Spectrometry (TIMS) is an invaluable tool in nuclear forensics as it enables isotopic assays of actinides to be measured, permitting analysis to include special nuclear material isotopic assays, nuclear reactor monitoring, and treaty verification. In one method of measurement for the TIMS system, samples are deposited in solution form on high-purity rhenium filaments. The filaments are heated to evaporate the solvent, and then further heated to cause sample ionization, permitting the sample to be transmitted through a magnetic field which separates ions based on mass to charge ratio into detectors for counting. Heavier ions will be deflected …


Neutron Displacement Damage In Germanium Tin Photodiodes, Nathan J. Gale Mar 2020

Neutron Displacement Damage In Germanium Tin Photodiodes, Nathan J. Gale

Theses and Dissertations

GeSn is a promising material for photodiodes in the near-to-mid infrared (IR) spectrum because of new growth methods that enable integration with complementary metal oxide semiconductor (CMOS) technology. While natural germanium has a threshold wavelength of 1800 nm, 6.9 Sn content extends the threshold wavelength to 2700 nm based on a Sn content dependent bandgap. Also, unlike other semiconductors that require liquid nitrogen cooling to act as an IR sensor, GeSn can be operated at room temperature, enabling a wide variety of applications. In this study, photodiodes ranging from 0 to 6.9 tin content were subjected to 1 MeV (Si) …


Rapid Analysis Of Plutonium Surrogate Material Via Hand-Held Laser-Induced Breakdown Spectroscopy, Ashwin P. Rao Mar 2020

Rapid Analysis Of Plutonium Surrogate Material Via Hand-Held Laser-Induced Breakdown Spectroscopy, Ashwin P. Rao

Theses and Dissertations

This work investigated the capability of a portable LIBS device to detect and quantify dopants in plutonium surrogate alloys, specifically gallium, which is a common stabilizer used in plutonium alloys. The SciAps Z500-ER was utilized to collect spectral data from cerium-gallium alloys of varying gallium concentrations. Calibration models were built to process spectra from the Ce-Ga alloys and calculate gallium concentration from spectral emission intensities. Univariate and multivariate analysis techniques were used to determine limits of detection of different emission line ratios. Spatial mapping measurements were conducted to determine the device's ability to detect variations in gallium concentration on the …


Determination And Simulation Of The Neutron Spectrum Of Nuclear Detonations And Surrogate Sources, Taylor M. Nichols Mar 2020

Determination And Simulation Of The Neutron Spectrum Of Nuclear Detonations And Surrogate Sources, Taylor M. Nichols

Theses and Dissertations

This research determined a methodology for characterizing the Fast Beam Facility (FBF) at The Ohio State University Nuclear Reactor Laboratory to test the response of photovoltaic arrays to nuclear weapon radiation. Additionally, this research developed neutron and gamma nuclear weapon output spectra of two environments for comparison to the FBF spectrum. A Bonner sphere spectrometer (BSS), coupled with the unfolding program Maximum Entropy Deconvolution (MAXED), was employed as a means of determining the energy spectrum of neutrons. Using the ISO 8529 americium beryllium (AmBe) source as the a priori default spectrum, MAXED was used to unfold the spectrum of neutrons …