Browsing by Author "Sudowe, Ralf, committee member"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Open Access A net-risk approach to displacement and reoccupation decision making(Colorado State University. Libraries, 2019) Braley, Gerald Scott, author; Johnson, Thomas E., advisor; Brandl, Alexander, committee member; Fisher, Gwen, committee member; Sudowe, Ralf, committee memberDecision makers and planners have a large body of information available concerning most aspects of a radiation disaster. International and national standards organizations, as well as national and local level policies and plans provide little guidance about the risks involved in relocating a population from a radiologically contaminated area. Populations displaced after all types of disasters have demonstrated poorer health outcomes, both physiological and psychological, than their non-displaced peers. These include a greater risk of diabetes and greater rates of post-traumatic stress disorder and depression when compared with other populations who experienced the disaster but were not relocated. Methodologies for population-level radiation dose prediction have improved, with recent data from contaminated areas in Japan providing real-world information about radiation doses. These improvements have not yet made their way into policies and guidance. The objective of this work is to quantify and incorporate multiple forms of risk, radiological and non-radiological, into a single model to improve decision making and minimize harm connected to displacement from and reoccupation of radiologically contaminated areas after a disaster.Item Open Access Development of a Bayesian linear regression model for the detection of a weak radiological source from gamma spectra measurements(Colorado State University. Libraries, 2021) Meengs, Matthew, author; Brandl, Alexander, advisor; Johnson, Thomas E., committee member; Sudowe, Ralf, committee member; Kokoszka, Piotr, committee memberThe detection of radiation requires the use of statistical tools due to the probabilistic nature of the emission and the interaction properties of radiation. Frequentist statistical methods are traditionally employed towards this end – the most common being the "traditional" method which calculates a decision threshold above which a source is determined to be present. The decision threshold is calculated from a predetermined false positive rate (typically 5%) and is used as a decision parameter. The decision parameter is a statistical tool by which it is determined whether or not a source other than background is present. In radiological conditions where a source is both improbable and weak, and where counting time is limited, the detection of a source becomes progressively more challenging using this traditional method. The detection of clandestine fissile materials presents such a challenge, and with the increasing risk of nuclear proliferation, there exists a growing motivation to research more optimal methods of detection, especially where a missed detection is of such high consequence. Previous research has been conducted on using a Bayesian model to develop a decision parameter for weak source detection. The use of a Bayesian model has been shown in laboratory settings to outperform the traditional frequentist method. However, the model tested was designed for gross counts only. In the present study, a Bayesian algorithm is being developed and tested that uses the entirety of the gamma spectrum. Specifically, several Bayesian linear regressions are developed and tested which compared different energy ranges in the spectrum. The parameters generated from these linear regressions are tested for their efficacy as decision parameters. With the additional information presented from the entire spectrum, it is theoretically possible that even further improvements in the detection of a weak source can be achieved. The results of this research have shown that regressor coefficients via a Bayesian method are effective as decision parameters. The best results, however, were shown only to match the efficacy of the more traditional, frequentist method of detection.Item Open Access Electron paramagnetic resonance dosimetry and the use of Japanese wild boar tooth enamel as a dosimeter for reconstruction of lifetime external absorbed doses from the Fukushima Exclusion Zone(Colorado State University. Libraries, 2018) Harshman, Amber, author; Johnson, Thomas E., advisor; Brandl, Alexander, committee member; Sudowe, Ralf, committee member; Fisher, Gwen, committee memberThe goal of this study was to establish characteristics of Japanese wild boar tooth enamel in the region of 0.25 – 12.0 Gy and to reconstruct external doses to wild boar native to the Fukushima Exclusion Zone using Electron Paramagnetic Resonance Dosimetry. The significance of Japanese wild boar in their ecosystem and their position within the trophic hierarchy make the wild boar a species of particular importance and therefore the focus of this study. Dose response, linearity, and variability of enamel originating from various wild boar were investigated. Radiation dose response of Japanese wild boar tooth enamel in the range of 0.25 – 12.0 Gy was found to be linear, and the average variation in dose response between teeth originating from the same boar specimen was 30%. Analysis of dose response of permanent and deciduous tooth enamel revealed a statistically significant difference in both the degree of dose response and also variation. No statistically significant difference in dose response was found in permanent molar teeth of boar of differing ages or in boar of different sex. Doses were successfully reconstructed with large associated uncertainties. The critical level dose value for the calibration curve was 1.0 Gy, and the detection limit dose was 1.8 Gy, suggesting that this method would be more beneficial for boar with lifetime doses over 1 Gy. The method of reconstructing external doses using EPR dosimetry with tooth enamel from Japanese wild boar as dosimeters has proven to be a viable method which can be used to reconstruct doses to wildlife in accident-stricken areas in the absence of alternative dosimetry.Item Open Access Inventory dynamics and soil factors affecting soil-to-plant ¹³⁷Cs transfers in Fukushima forest ecosystems(Colorado State University. Libraries, 2020) Zhang, Jian, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Sudowe, Ralf, committee member; Pilon-Smits, Elizabeth, committee memberThe objective of this study was to understand the soil factors affecting soil-to-plant transfer factors in understory plant species as well as their contribution to the total 137Cs inventory in aboveground biomass within the Fukushima forest ecosystem. Radiocesium contamination from the March 2011 accident at the Fukushima Da-ichi Nuclear Power Station (FDNPS) was initially deposited on the forest canopies with deposition into the soil occurring over the next few years through litterfall and precipitation. Measurements taken from the Yamakiya site in 2014 show that the contribution of understory plants to the total inventory of radiocesium in aboveground biomass was very low compared to the dominant Japanese cedar trees. However, measurements were not taken in other affected sites within Fukushima prefecture as well as potential change in concentrations of radiocesium in understory biomass since 2014. Data for evaluating the transfer factors was obtained through sampling of soil and understory plants at the Yamakiya, Tsushima, Tomioka, Okuma, and Yokomuki sites inside Fukushima Prefecture. Both 134Cs and 137Cs measurements were collected, however 134Cs concentrations were negligible compared to 137Cs so only 137Cs data was considered. 137Cs content was determined using gamma spectroscopy of the soil and plant samples and to find the concentration of bioavailable 137Cs within the root profile of the understory plants as well as 137Cs concentration within the understory plant itself. The soil and plant 137Cs concentration was used to determine the soil-to-plant uptake factors for the sampled understory species as well as the contribution of the understory plants to the total 137Cs inventory in aboveground biomass. The effect of soil exchangeable [K+], exchangeable [Cs+], exchangeable 137Cs activity concentration, total 137Cs activity concentration, and pH on 137Cs uptake by understory plants was determined through the soil-to-plant uptake factors at the various sample sites. The same data was used to find the 137Cs deposition in the soil, 137Cs inventory in Yamakiya, and patterns between plant activity concentration between plant species. Soil measurements showed a logarithmic decrease in 137Cs activity concentration with decreasing soil depth. Measurements also supported a 4.39 year effective half-life using GIS and Nuclear Regulatory Authority data, however using IER data a radiological half-life of 30.17 years was supported instead. The majority of 137Cs inventory in Yamakiya was found to be in soil (80.54%) and trees (18.52%) with understory plants making up a negligible contribution. This contribution by trees was much higher than the one found in previous years. For understory plants, it was found that there are higher 137Cs activity concentrations in the more metabolically active portions of the plants. 137Cs was a significant contributing factor across all understory plant species in predicting the soil to plant transfer factors. The ability to properly estimate the activity concentration of understory plants using only the one soil factor can contribute to faster estimation of potential 137Cs concentrations in plants or uptakes by herbivores in areas contaminated by 137Cs. The further understanding of 137Cs dynamics in forest ecosystems will assist in creation of a long-term forest radiation contamination management strategy.Item Open Access Investigation of tritium atom exchange in plastic liquid scintillation vials(Colorado State University. Libraries, 2018) Wang, John Jen-Chiang, author; Brandl, Alexander, advisor; Sudowe, Ralf, committee member; Walrond, John, committee memberTritium is a naturally occurring radionuclide; it is an analyte of interest in many air, soil, and water samples. It has been shown that long term storage and study of tritium samples results in a reduction in tritium activity not attributed to the natural radioactive decay. Several explanations have been offered through past literatures including diffusion, LSC cocktail degradation, and change in quenching effects. Another possible explanation for the decrease in activity is that tritium may have been organically bound to the plastic possibly due to exchangeable hydrogen atoms along the plastic carbon chain. The hypothesis that tritium can be incorporated into the plastic, interchanging the 1H atoms in the plastic with 3H atoms, was experimentally tested. The experiment consisted of adding deionized water into a previously used plastic vial which had contained tritium to determine if the deionized water had now become tritiated. The results showed that the longer the tritiated water is stored in the vials, the greater the loss of tritium activity in plastic vials is compared to glass vials. An increase in the time that the tritiated water is stored also increases the activity of the tritium found in the deionized water in plastic vials but not in the glass vials. The combination of these two observations supports the hypothesis that tritium exchange may have occurred between the tritiated water and the hydrogen within the plastic vials.Item Open Access Model based analyses of the cesium dynamics in Pond 4, Savannah River Site(Colorado State University. Libraries, 2018) Miller, Vivien, author; Johnson, Thomas E., advisor; Brandl, Alexander, committee member; Sudowe, Ralf, committee member; Hoeting, Jennifer, committee memberTo view the abstract, please see the full text of the document.Item Open Access Monte Carlo determination of detection efficiency for portal monitoring(Colorado State University. Libraries, 2024) Blair, Noah Jeffrey, author; Brandl, Alexander, advisor; Sudowe, Ralf, committee member; Jeckel, Kimberly, committee memberAt ports of entry into the country, at high security events such as political or athletic gatherings of crowds, and at high risk locations, portal monitors are used to detect the presence of ionizing radiation and ensure radiological/nuclear materials do not fall out of regulatory control or are utilized with malicious intent. This work uses computer models to determine the probability of photon radiation being detected in polyvinyl toluene, a plastic scintillator material, for a range of source energies, truck positions relative to the detector, and cargo materials. These results are used to develop models for operators of portal monitors to predict the activity of a radioactive source given the measured count rate and integrated count measurements. A linear model of the detection efficiency produces an analytic expression of the measured count rate given the emission spectrum of a source which allows for calculation of net counts between two points on the truck's trajectory and the time derivative of the count rate. The time derivative of the count rate has a similar characteristic behavior along the truck's trajectory and has the potential to be an indicator of weak radiological sources. A MARS model allows for accurate prediction of the net count rate for truck positions and source energies not directly modeled. These models best predict detection efficiency for higher energy photons and are primarily useful for the prediction of detection of fission and activation products.Item Open Access Radiation dose to veterinarians and veterinary technicians during performance of radioiodine treatment of Felis catus(Colorado State University. Libraries, 2021) Dieffenthaller, Meghan Marie, author; Johnson, Thomas, advisor; Sudowe, Ralf, committee member; Pagliassotti, Michael, committee memberThe purpose of this project is to determine I-131 uptake of veterinarians or veterinary staff when radioiodine (I-131) is administered via injection to domesticated cats (Felis catus) with hyperthyroidism. Currently, veterinarians and staff perform a bioassay either every three months or if they have administered a cumulative 10 mCi of I-131. Veterinarians and staff undergo specific training for the handling of radioiodine injection of cats to minimize and prevent an intake. A bioassay is performed post cat injection to determine if I-131 was inhaled or absorbed. The frequency of these bioassays requires dedicated time of the veterinarians and those who must perform the bioassay. Bioassay data from veterinarians and staff at the Colorado State University Veterinary Teaching Hospital (CSU VTH) administering I-131 from the past 20 years were analyzed to ascertain if there is a correlation between the amount of time elapsed between the I-131 administration and the bioassay and the net counts resulting from the bioassay. The amount of I-131 administration and the bioassay net counts were also analyzed to determine if there was a correlation. No correlations were found, and out of 168 I-131 administrations over 20 years, only 7 bioassays showed measurable doses of I-131 of a committed dose equivalent (CDE) of 5.71 mrem (n=1), 7.53 mrem (n=2), 10.9 mrem (n=1), 20.7 mrem (n=1), and 75.1 mrem (n=2). The current precautions taken to prevent the intake of I-131 appear sufficient enough to allow for less frequent bioassays.Item Open Access Radiocesium soil to understory plant transfers in Fukushima forests(Colorado State University. Libraries, 2018) Workman, Daniel, author; Johnson, Thomas, advisor; Sudowe, Ralf, committee member; Omur-Ozbek, Pinar, committee memberThe objective of this research was to investigate the activity of radiocesium in plants and soil found in forested areas near the Fukushima Dai-Ichii Nuclear Power Station (FDNPS). Plant samples and 15-cm soil core samples were collected at four sampling locations. The quantity of soluble and exchangeable amounts of 137Cs in soil was measured by performance of two sequential extractions using de-ionized water and ammonium acetate respectively. The remaining radiocesium bound to the soil following the extractions was considered strongly bound to soil particles and whose movement into either soluble or exchangeable concentrations is slow. The distribution of the different forms of radiocesium were developed throughout each 15-cm soil core as measured using a High Purity Germanium Detector (HPGe). An analysis of correlation between plant activity versus plant root area and exchangeable radiocesium resulted in limited success. It remains probable that quantifying plant root radiocesium distribution can aid in predicting plant uptake, but it is believed that the concentrations of competing ions in soil should also be quantified and parameterized as well as additional possible routes of intake (throughfall). Concentration ratios (137Cs plant activity/137Cs soil activity) of 12 plants were calculated and exhibited a broad range from 0.01 to 2.5. The broad range of plant concentration falls within the International Atomic Energy Agency Parameter Handbook values of herbaceous plants in clay soils. Concentration ratios appear similar within sampling locations which suggests that additional soil characteristics (clay content, competing ions) can be used to describe plant uptake of radiocesium.