Browsing by Subject "Radioxenon"
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Item A method for measuring radioxenon emanation with cryotrapping and γ spectroscopy(2018-05-07) Blood, Mikaela E.; Haas, Derek Anderson, 1981-; Biegalski, Steven R.Measuring noble gas emanation has been challenged by environmental variables that greatly impact the behavior of gas transport such as temperature, pressure gradients, and complex geologies. A method has been developed to eliminate environmental variables and diffusive transport to obtain a direct measurement of radioxenon’s emanation coefficient, K. The Emanation Measurement Apparatus (EMA) utilizes neutron activation and a cryotrapping technique with LN₂, which increased gas trapping efficiency from 4 ± 3 % to 78 ± 7 %. K values are measured by γ spectroscopy with a Hyper-Pure Germanium detector. Preliminary tests demonstrated the capability of this new process to make reproducible emanation measurements with quantifiable uncertainty. The results measured U₃O₈ radioxenon emanation coefficients of 0.016 ± 0.002 for ¹³³Xe and 0.025 ± 0.002 for ¹³⁵Xe . The experiments consistently resulted in a higher K value for ¹³⁵Xe and this is speculated to be an effect of recoil emanation. The results suggest that all radioxenon isotopes do not have equal fractional release rates at moderate temperatures.Item Advancements in radionuclide monitoring technologies used to detect indications of nuclear explosions(2017-05-05) Wilson, William Hamill, 1983-; Biegalski, Steven R.; Haas, Derek; Landsberger, Sheldon; Lowrey, JustinThe objective of the research documented in this dissertation was to advance the state-of-the-art radionuclide monitoring technologies used to detect indications of nuclear explosions, which are absolutely prohibited by the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Advancements are made in two areas. The first advancements are in the characterization and optimization of a Si-PIN diode-based radiation spectrometer prototype sensitive to both photons and conversion electrons. A novel peak-fitting algorithm referred to herein as the WiPFA algorithm was developed to support the Si-PIN diode spectrometer prototype characterization efforts. The absolute conversion electron detection efficiency of the prototype was found to be 5.2 ± 0.4 % at conversion electron energies near 150 keV, and the [superscript 131m]Xe, [superscript 133m]Xe, ¹³³Xe, and ¹³⁵Xe Minimum Detectable Concentrations (MDCs) were found to be 1.7, 2.0, 2.1, and 56 mBq-m⁻³, respectively. A series of Monte Carlo N-Particle (MCNP) radiation transport code models were then developed to evaluate the MDCs associated with a series of optimized Si-PIN diode-based spectrometer designs. These optimization studies revealed that coupling Si-PIN diodes available today with thinner, cylindrical spectrometer designs could reduce the [superscript 131m]Xe, [superscript 133m]Xe, and ¹³³Xe, MDCs to 0.48, 0.57, and 0.58 mBq-m⁻³, respectively. Subsequent studies utilizing larger, thicker Si-PIN diodes indicated that additional reductions down to 0.31, 0.37 and 0.37 mBq-m⁻³ might be possible. These small radioxenon MDCs coupled with other perceived advantages of Si-PIN diodes suggest that Si-PIN diode-based radiation spectrometers could serve as attractive alternatives to the high-resolution gamma-ray and beta-gamma coincidence spectrometers currently employed by the verification regime of the CTBT. The second area in which advancements are made is the radionuclide background activity concentration characterization area. The focus here is on CTBT-relevant radioactive particulates and noble gases produced via spontaneous fission and via naturally occurring cosmic-ray induced fission and activation reactions. A new application—the Terrestrial Xenon and Argon Simulator (TeXAS) application—was developed to streamline and automate the creation of high-fidelity MCNP models and dedicated nuclear data libraries required to support detailed, site-specific background activity concentration characterization studies. The capabilities of the TeXAS application are demonstrated and used to develop background activity concentration estimates specific to several layers of the Earth’s atmosphere, several subsurface depths in six geologies prevalent in the Earth’s upper crust, and seawater.Item Comparison of the phoswich and ARSA-type detectors for radioxenon detection(2010-05) Ward, Rebecca Morgan; Biegalski, Steven R.; Haas, DerekThe Comprehensive Nuclear Test Ban Treaty verification regime mandates atmospheric monitoring for the four radioxenon isotopes that are produced in high abundance in a nuclear explosion: [superscript 131m]Xe, [superscript 133m]Xe, [superscript 133g]Xe, and [superscript 135g]Xe. This mandate has driven the development of improved xenon detectors, including a phoswich detector, which has potential to replace the ARSA detector in the International Monitoring System. In this experiment, the four relevant radioxenon isotopes were produced through neutron activation and the phoswich detector was used to attain spectra from the gas. Spectral characteristics and resolution of the phoswich spectra were compared to an ARSA-type [beta]-[gamma] coincidence detector to perform an overall evaluation of the phoswich detector. The results indicated that spectral characteristics and resolutions for the phoswich were comparable to the ARSA-type detector, with slightly improved beta detection. As an additional test of the new detector's capabilities, a tailored spectrum designed to mimic a nuclear explosion signature was produced and analyzed with the detector.Item Development of a cryogenic tracer irradiation facility(2021-07-16) Lester, Ryan Stuart; Haas, Derek Anderson, 1981-The goal of this thesis is to provide instruction on the design, modeling, construction, and implementation of a cryogenic tracer irradiation facility that produces isotopically pure noble gas samples both efficiently and cost effectively. These samples will be used for various research purposes. This facility will be installed into Beam Port 1 (BP1) of The University of Texas at Austin’s Nuclear Engineering Teaching Lab (NETL) TRIGA Mark II reactor core. This work builds on previous creation of noble gas activities of ¹²⁷Xe and ³⁷Ar on the order of 3.7x10¹⁰ Bq (1 Ci). These were produced through the activation of ¹²⁶Xe and ³⁶r, respectively, in the 3-Element facility which sat within the reactor core. This new facility offers means to produce these tracer gases in ways that are much safer and more cost-effective. Methods developed include solidification of the respective gases to increase sample density, change of location, and new facility components. The most important aspect of the design is the changes made to increase sample density by way of cryogenically freezing the gases onto a condenser. Beam Port 1 was chosen because it is larger than the in-core facilities and provided a safer location than in the core itself in the event that the pressure safety limit was exceeded. To efficiently freeze these gases a condensing system was designed and built by Cryomech Inc. The condensing system is composed of an irradiation canister, heat exchanger, helium compressor and transfer lines, and gas transfer lines.Item Examination of natural background sources of radioactive noble gases with CTBT significance(2013-12) Johnson, Christine Michelle; Biegalski, Steven R.For verifying the Comprehensive Nuclear-Test-Ban Treaty (CTBT), different monitoring technologies (seismic, infrasound, hydroacoustic, and radionuclide detection) are combined. The monitoring of radioactive xenon isotopes is one of the principal methods for the determination of the nuclear nature of an explosion. After an underground nuclear detonation the radioxenon isotopes [superscript 131m]Xe, [superscript 133m]Xe, ¹³³Xe, and ¹³⁵Xe, and the radioargon isotope ³⁷Ar have an increased probability of detection. In order to effectively utilize these isotopes as indicators of nuclear testing, an accurate background must be calculated. This work examines the fission products produced by spontaneous fission of ²³⁸U, which is naturally present in the earth's crust, and of ²⁴⁰Pu which is present as a product of nuclear weapons and nuclear reactor accidents. These calculations provide a range of production values for radioxenon in a variety of geologies as well as at various historic locations. The activation of geologic calcium and potassium by cosmic ray neutrons is considered for a variety of properties effecting the neutron flux. These calculations provide a range of radioargon production values across a selection of geologies. The impact of latitude and the solar activity cycle are also examined. In order to examine the transport of the isotopes through soil a model of the transport of xenon and argon through various geologies was developed. This model incorporates both the introduction of xenon from the atmosphere and that produced by spontaneous fission. This is then considered in light of what might be observed in an on-site inspection (OSI). What this work finds is that the radioxenon natural background does exceed detection limits in particular locations and geologies, however, a careful examination of the location and the ideal sampling depths can minimize the impact during an OSI. Radioargon, however, has a much larger natural background at shallow depths which are the realm of OSI sampling. Should radioargon sampling be used in an OSI the sampling time is crucial in distinguishing a nuclear explosion from the natural background. In some scenarios the natural background production of radioargon may be sufficient to interfere with the detection of an underground nuclear weapon test. This information may be beneficial in the development of future OSI noble gas monitoring techniques.Item Mitigation of the radioxenon memory effect in beta-gamma detector systems by deposition of thin film diffusion barriers on plastic scintillator(2010-12) Fay, Alexander Gary; Biegalski, Steven R.; Haas, DerekThe significance of the radioxenon memory effect in the context of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty is introduced as motivation for the project. Existing work regarding xenon memory effect reduction and thin film diffusion barriers is surveyed. Experimental techniques for radioxenon production and exposure, as well as for thin film deposition on plastic by plasma enhanced chemical vapor deposition (PECVD), are detailed. A deposition rate of 76.5 nm min⁻¹ of SiO₂ is measured for specific PECVD parameters. Relative activity calculations show agreement within 5% between identically exposed samples counted on parallel detectors. Memory effect reductions of up to 59±1.8% for 900 nm SiO₂ films produced by plasma enhanced chemical vapor deposition and of up to 77±3.7% for 50 nm Al₂O₃ films produced by atomic layer deposition are shown. Future work is suggested for production of more effective diffusion barriers and expansion to testing in operational monitoring stations.Item Production and analysis of traditional and non-traditional radioxenon isotopes(2015-05) Klingberg, Franziska Julietta; Biegalski, Steven R.; Biegalski, Kendra M.F.; Haas, Derek A.; Landsberger, Sheldon; Saey, Paul R.J.; Schneider, ErichRadioxenon releases can originate from fission during nuclear detonations (atmospheric, underground, and underwater), research and commercial reactors, and medical isotope production facilities. Their impacts on atmospheric sample analysis have to be well understood to distinguish between clandestine activities and commercial operations. The global community relies on atmospheric monitoring of radioxenon, among other technologies, to monitor emissions from underground nuclear tests. The Comprehensive Nuclear Test-Ban Treaty (CTBT) incorporates radioxenon monitoring within International Monitoring System (IMS) with a focus on the traditional radioxenon isotopes ¹³¹ [superscript m] Xe, ¹³³ [superscript m] Xe, ¹³³Xe, and ¹³⁵Xe. To strengthen environmental monitoring for radioxenon, a method to produce high purity radioxenon samples was developed. The University of Texas’ 1.1 MW TRIGA research reactor was used for radioactive sample production via neutron activation. The reactor facilities include a pneumatic system for precise timing when irradiating samples. In order to use the pneumatic facilities, gaseous samples have been encapsulated in quartz to fit into the polyethylene vials designed for the system; this method also minimizes leakage, and avoids contaminants from entering the sample. Enriched, stable, isotopically pure xenon gas was irradiated with neutrons in order to activate it to radioxenon isotopes, yielding a complete set of radioxenon isotopes including non-traditional – ¹²⁵Xe, ¹²⁷Xe, ¹²⁹ [superscript m] Xe, ¹³⁵ [superscript m] Xe and ¹³⁷Xe – and traditional radioxenon isotopes. The samples were analyzed with a β--γ coincidence detector; the measurement of the non-traditional isotopes in an ARSA-style β--γ coincidence detector were the first of their kind. Measurements of the ¹³¹ [superscript m] Xe, ¹³³ [superscript m] Xe, ¹³³Xe, and ¹³⁵Xe were used to determine the β--γ coincidence efficiency of the detector and the metastable versus ground state production ratio after irradiation of ¹³³Xe and ¹³⁵Xe. Regions of interest (ROI) were defined for ¹²⁵Xe, ¹²⁷Xe, ¹²⁹ [superscript m] Xe, and ¹³⁷Xe to estimate their interference with the traditional isotopes. The newly defined ROIs aid in distinguishing between radioxenon signatures originating from fission and those mainly originating from neutron activation, thus advancing atmospheric sample analysis in the context of CTBT verification.Item Production and subsurface vertical transport of radioxenon resulting from underground nuclear explosions(2010-12) Lowrey, Justin David; Biegalski, Steven R.; Deinert, MarkAtmospheric monitoring of radionuclides as part of the International Monitoring System requires the capability to differentiate between a radionuclide signature emanating from peaceful nuclear activity and one emanating from a well-contained underground nuclear explosion. While the radionuclide signatures of nuclear weapons are generally well known, radionuclides must first pass through hundreds of meters of earth to reach the surface where they can be detected and analyzed. Less well known is the affect that subsurface vertical transport has on the isotopic signatures of nuclear explosions. In this work, a model is developed, and tested, simulating the detonation of a simple underground nuclear explosion and the subsequent vertical transport of resulting radioxenon to the surface. First, the fast-fission burn of a fissile spherical core surrounded by a layer of geologic media is modeled, normalized to 1 kton total energy. The resulting source term is then used in the testing and evaluation of the constructed vertical transport model, which is based on the double-porosity model of underground fluid transport driven by barometric pumping. First, the ability of the vertical transport code to effectively model the underground pressure response from a varying surface pressure is demonstrated. Next, a 100-day simulation of the vertical migration of a static source is examined, and the resulting cumulative outflow of roughly 1% initial inventory outflow per cycle is found to closely follow the analytical predictions. Finally, calculated radioxenon source terms are utilized to model the resulting vertical transport and subsequent surface outflow. These results are found to be consistent with the physical expectations of the system, and lastly a cursory sensitivity analysis is conducted on several of the physical parameters of the model. The result is that the vertical transport model predicts isotopic fractionation of radioxenon that can potentially lie outside of currently accepted standard bounds.Item Radioxenon emissions abatement system for molten salt research reactor’s impact on nuclear explosion monitoring(2020-05-07) Kowalczyk, Joseph Edward; Haas, Derek Anderson, 1981-Radioxenon is produced from emissions due to nuclear explosion testing and civilian sources—nuclear power plants and medical isotope facilities. Radioxenon emissions are monitored around the world by the International Monitoring System (IMS) for treaty verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). As most of the current fleet of Light-Water Reactors (LWR) will be nearing the end of their lifespan in the mid-2030s, the next generation of nuclear power reactors are being developed. One type of these next-generation reactors, molten salt reactors (MSR), and their chemical reprocessing facilities have the potential to release significant quantities of radioxenon, thus, impeding the Comprehensive Nuclear-Test-Ban Treaty Organization’s (CTBTO) ability to monitor for nuclear explosion testing. This research looked at designing an abatement system for a future 1MW MSR research reactor and its implications for nuclear explosion monitoringItem Transport and sorption of noble gases in porous geological media(2017-05) Paul, Matthew John; Biegalski, Steven R.; Haas, Derek; Landsberger, Sheldon; Lowrey, JustinThe transport of noble gas radionuclides in porous media is critical to the detection of underground nuclear explosions as well as the sequestration of reprocessing off-gases. However, in field tests releasing radioxenon underground, the quantity of radioxenon observed at the surface has fallen well below expectations. This research has examined the diffusivity and sorption of noble gases (Ar, Kr, and Xe) and the inert molecular gas sulfur hexafluoride (SF₆) in both dry and wet porous media seeking a plausible mechanism for this discrepancy. In support of this, the two-bulb method for estimating diffusivity has been modified for experimentation in porous media. To replicate underground transport conditions, low-level concentrations of the tracer gas species were required. Detecting trace quantities of these inert species necessitated the development of precision gas chromatography-mass spectrometry (GC-MS) capabilities for these permanent gases. This was accomplished through the use of internal standards; atmospheric nitrogen, which contains the scarce isotope ¹⁵N, and synthetic carbon tetrafluoride, CF₄, were both utilized. Both internal standards were shown to be capable of producing acceptable results under ideal conditions, but the CF₄ method showed more resiliency. The results of the diffusivity trials demonstrated the adequacy of the porosity-tortuosity factor model for both dry and wet macroporous media. However, in both the dry and wet trials, the equilibrium concentration of Xe converged at a lower fraction of initial concentration than the other tracer gases considered. The deviation in equilibrium fraction is expected in the wet trial due to the increased solubility of Xe versus the other tracer species. However, deviation in the dry trial necessitates consideration of adsorption effects. While the physical adsorption of Xe on shale formations has been considered as a potential mechanism for the scarcity of primordial Xe isotopes in the atmosphere, adsorption measurements were conducted on a range of materials demonstrating not only the relative strength of xenon adsorption over other noble gases, but also that the magnitude of this effect readily exceeds that of solubility. Consequently, with the observation of significant gas adsorption, consideration of adsorbed phase accumulation is necessary when scaling to larger geological systems.