Mountain Scholar :: Browsing by Author "Johnson, Thomas, advisor"

Browsing by Author "Johnson, Thomas, advisor"

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Open Access
A comparison of methods to derive aggregated transfer factors: tested using wild boar data from the Fukushima prefecture
(Colorado State University. Libraries, 2017) Anderson, Donovan, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Hess, Ann, committee member
In March of 2011, the Fukushima Daiichi disaster released airborne radioactive material dominated by Cs-134 and Cs-137. When the radionuclides settled, they contaminated soil and plants, with wild boar also becoming contaminated through various pathways. An estimate of the radiocesium concentration in wild boar tissues can be obtained from an aggregated transfer factor based on soil contamination levels. The aggregated transfer factor (Tag) for purposes of this study, is the ratio of Cs-137 concentration in wild boar tissues (Bq kg-1) divided by the Cs-137 surface contamination of soils (Bq m-2). In this study, two methods were used to estimate the Tag values, and a comparison was made to determine which method reduced uncertainty. Both methods rely on harvesting and measuring radiocesium in wild boar tissues (bicep femoris muscle). The radiocesium value used for soil, however, was different in the two methods. One was obtained from a public database of samples collected by the Japanese government in 2015. Oftentimes, the soil sample paired with the wild boar trap site were not within the home range of the wild boar, reducing accuracy of the predicted radiocesium concentration levels in the animal. The other method used soil samples collected at the point of wild boar capture. The purpose of this study is to ascertain if the use of the database radiocesium soil concentration values is of sufficient granularity to provide a useful estimate of Tag values. The mean Tag value calculated in the Fukushima prefecture for wild boar were 2.3×10-3 m2 kg-1 fresh weight. The research revealed that the database radiocesium concentration values for soil (Bq m-2) used in calculating aggregated transfer factors, do not accurately represent the containment levels in the wild boar. Collecting soil samples within the home range of the animal reduces uncertainty in calculating Tag values to estimate whole body contamination levels of a wild boar. Our data complements and supports the existing monitoring programs conducted by the National and Prefecture governments in Japan by showing lower concentrations of cesium in soil and wild boar within decontaminated areas.
Open Access
A comparison of the use of sodium iodide and lanthanum bromide scintillation crystals for airborne surveys
(Colorado State University. Libraries, 2014) Bailey, Derek M., author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Milton, Stephen, committee member
The Environmental Protection Agency (EPA) Aerial Spectral Environmental Collection Technology (ASPECT) program performs aerial radiological and chemical characterization of geographical regions of interest. Airborne surveys are performed to characterize environmental radionuclide content, for mineral exploration, as well as for emergency scenarios such as major releases or lost sources. Two radiological detection systems are used by the ASPECT team for gamma-ray detection and characterization: lanthanum bromide [LaBr3(Ce)] and sodium iodide [NaI(Tl)] scintillation systems. An aerial survey of a uranium mine in the western United States was performed using both NaI(Tl) and LaBr3(Ce) detection systems. Analyses of the survey data were performed with RadAssist software and applying International Atomic Energy Agency (IAEA) airborne gamma ray mapping guidelines. The data for the survey were corrected for cross-over, which is spectral interference from higher energy photons as a result of Compton scattering, height attenuation, cosmic ray contribution to signal, and Radon contribution to signal. Two radiation survey contours were generated from each discrete data set. Based on analysis of the uranium mine survey results, LaBr3(Ce) produced a product comparable to that of NaI(Tl). The LaBr3(Ce) detection system contained 1/16th the scintillating volume and had a total system weight that was 1/4th that of the NaI(Tl) system. LaBr3(Ce) demonstrated a clear advantage over NaI(Tl) detectors in system mobility, and weight factors in airborne gamma ray spectroscopy.
Open Access
Analysis of potential airborne radionuclide emissions during and after fires through contaminated soil areas on the INL
(Colorado State University. Libraries, 2021) Williams, Connor, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Lindsay, James, committee member
The risk of wildfires burning through legacy soil contamination areas of the Idaho National Laboratory (INL) facility with consequent airborne radiological releases has been a concern for some time and this concern has only increased in recent years with an increasing number and size of wildfires burning through the property. The question of personnel safety has been raised in terms of firefighters and other first responders who might be in close proximity to an ongoing fire as well as the health risks to facility staff and members of the general public. As a result, this study seeks to update the current soil nuclide inventory of the known legacy contamination sites which pose a fire risk as well as update previous fire resuspension studies made of INL contamination sites through the use of updated modeling techniques and inputs available in more recent literature. Baseline soil contamination values were developed for the contaminated areas starting with average measured radionuclide concentrations in soil, using in-situ gamma spectroscopy or decay correcting the best available data from previous reports. Soil-to-plant uptake fractions from the literature were used to estimate radionuclide concentrations in plants growing on the sites. Worst case estimates of plant biomass were used to yield release estimates during a fire. Doses to first responders or other high-exposure individuals were estimated through a comparison to the minimum soil screening concentrations calculated specifically for the INL facility in the literature. This study involved using dynamic dispersion models to determine the minimum soil and plant concentration, for various common nuclides found at INL, which would be necessary to produce an exposure of 10 mrem or greater either during a fire due to release of radionuclides from plant tissue, or after a fire due to resuspension of rootless soil. Based on the relatively low level of soil radionuclide concentrations in even the most contaminated sites, the low soil-to-plant transfer coefficients of the specific measured nuclides remaining in the soil and the likely quick dispersion and dilution of any released nuclides in the smoke/dust column, the overall exposure is likely to be small. Therefore, it is hypothesized that that any measurable radiological doses which could be expected to any given individual would be well below current occupational or public exposure limits and thus would not present a health hazard.
Open Access
Calibration of an irradiation facility
(Colorado State University. Libraries, 2017) Marcinko, Rion, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Duncan, Colleen, committee member
The objective of this research is to provide accurate reliable data for use in an irradiation facility and present findings in a manner useful to operators. The intended use of the irradiator and irradiator protocols dictate a need for a well-known administered dose. Dose rates from two independent methods were investigated at multiple distances away from the source. First, the irradiation platforms were examined for "hot spots" using Gafchromic © film to provide a qualitative estimate of the dose distribution. A quantitative assessment of doses was then performed using Fricke dosimetry (a primary standard). Finally, MCNP modeling was used to simulate irradiation at the various measured points and intermediate points in the radiation field. The results were used to provide dose rates within the radiation field for future researchers, and demonstrated how precision and accuracy vary using theoretical (MCNP) and measurement methodology. MCNP simulation matched the Fricke measurements within 10% for the first two positions explored, then diverged upon further movement from the source.
Open Access
Characterization of mixed linear energy transfer environments utilizing tissue-equivalent proportional counters
(Colorado State University. Libraries, 2023) Fehrman, Joseph M., author; Brandl, Alexander, advisor; Johnson, Thomas, advisor; Carlson, Kenneth, committee member
There is currently great interest in the biological impact of radiological space exposures due to manned space missions (e.g., moon) where astronauts will face the challenge of living on board spacecraft for long periods of time. Cosmic radiation of many types exists in space and creates a unique mixed linear energy transfer (LET) environment. A tissue equivalent proportional counter (TEPC) was used to produce dose-equivalent measurements and quantify neutron exposures. Three neutron sources were used to simulate high energy, mixed LET environments: californium-252, a plutonium-beryllium source, and a deuterium-tritium neutron generator. TEPC dose-equivalent measurements can be utilized for basic research, and regulatory or clinical purposes for correlation with observable health effects. The main study was to quantify and compare TEPC dose equivalent rates in microdosimetric volumes to determine if significant dosimetric differences exist between mixed LET environments generated by photons and neutrons. The findings from this experiment showed that mixed LET environments where both photons and neutrons interacted with the TEPC had lower average LET values than neutron-only exposures, and produced varying dose equivalent rates that were dependent on the source characteristics. In summary, the TEPC was capable of monitoring in a mixed-LET environment and was successful at measuring the absorbed dose of high-energy photon and neutron interactions in space-like settings.
Open Access
Contribution of ²³⁸U and ²³²TH to radiation dose and risk from fly ash effluent of coal-fired power plants
(Colorado State University. Libraries, 2010) Beckfield, Felicity Cunningham, author; Johnson, Thomas, advisor; Woody, Robert, committee member; Volckens, John, committee member
The goal of this project was to determine the activity concentrations of 238U and 232Th emitted from a coal-fired power plant that could potentially impact human health and the environment. The activity concentration of 238U and 232Th in fly ash was used to estimate effluent uranium and thorium. The estimate of effluent activity was then used to model radiation dose and evaluate any associated increase in cancer risk to employees working in the plant and individuals living near the plant. Grab samples of fly ash were obtained and manually fractionated using the soil sizing techniques of sieving and pipetting. The respective samples were counted using alpha spectroscopy to determine the activity concentrations of 238U and 232Th. Whole body dose was calculated using 10 CFR 20 Appendix B annual limits on intake (ALI). The alpha emissions from 238U and 232Th are of particular interest as they are significant contributors to dose in the lungs and other tissues due to their high relative biologic effectiveness and short range. The results of this study indicate that fly ash contains both 238U and 232Th but is not a radioactive substance as defined by the IAEA transportation safety standards and Title 49 of the Code of Federal Regulations. Although the relative concentration of radionuclides in the fly ash of this study is quite low, it is still possible for individuals to receive a measurable dose. Exceeding occupational and public dose limits would require inhalation of approximately 1-1000 kg of fly ash for 232U and approximately 50 g to 20 kg for 232Th. The highest CEDE (ICRP 30) per unit mass incurred by inhalation of fly ash was class W 232Th (1.81 mrem g-1), while class W 238U had the lowest CEDE per unit mass (3.32 prem g-1). The general relationship between activity concentration of 238U and 232Th found using data from radiochemical analysis and particle size suggest that activity concentration increases with increasing particle size. However the relationship between activity concentration and particle size found in the literature suggests that activity concentration increases with decreasing particle size. The accompanying health risk from 238U and 232Th in fly ash is predicted to be less than 10-5 percent.
Open Access
Design of a Compton scatter based radiation tracking system
(Colorado State University. Libraries, 2015) Healy, Heather, author; Brandl, Alexander, advisor; Johnson, Thomas, advisor; Lindsay, James, committee member
Gamma spectroscopy is one of the most common techniques used for the detection of radiologic materials. This technology is deployed in a variety of scenarios such as emergency response, monitoring, and the recovery of lost, stolen, or otherwise unaccounted radiologic material. In most practical scenarios, it is useful to know the location of a source in relation to a detector, in addition to the classic output from gamma spectrometers such as decay rate and energy peak information. In collaboration with the Remote Sensing Laboratory (RSL) at Andrew's Air Force Base, a novel detector design by RSL, which utilizes a 360° detectable range in order to increase the probability of remote detection, was investigated for the possibility to recreate source location information from Compton scattering events within the detector. A recreation of this novel detector is simulated using Geant4 to determine the optimal dimensions of sodium iodide detectors that produce the most single Compton scattering events in order to facilitate source location through the back-projection of Compton scattering angles. The optimal detector dimensions are determined by maximizing the number of single Compton scatter events and minimizing the percentage of Compton events that undergo multiple successive scatters in detectors of varying thicknesses and lengths. The optimal detector thickness was chosen to be 1.88 in, and the optimal detector length was chosen to be 4 to 4.5 in. In future projects, these optimized detectors can be used to apply suggested back-projection algorithms in order to determine the feasibility and functionality of this detector design for the purpose of radiologic source location.
Open Access
Detection of a weak radiological source in ambient background using spectral analysis
(Colorado State University. Libraries, 2018) Meengs, Matthew Richard, author; Brandl, Alex, advisor; Johnson, Thomas, advisor; Kokoszka, Piotr, committee member
The detection of radiation requires the use of statistical tools due to the probabilistic nature of the emission and interaction properties of radiation, an analysis that includes the testing of a hypothesis regarding the presence or absence of a source against background. Traditionally, a false positive rate of 5% is used to calculate a y*, the decision threshold, above which a source is determined to be present. However, in radiological conditions where a source is both improbable and weak, and where counting time is limited, detection of a source becomes increasingly 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 desire to research more optimal methods in detecting these sources, especially where a missed detection is of such high consequence. Previous research has shown that using a string of measurements, and calculating a detection limit based on a certain number of false positives within that string, consistently outperforms the traditional method of basing the detection limit on just one measurement. Such research to date has only been applied to counts of all energies (gross counts). The purpose of this research is to apply the success of this new detection algorithm to certain energies within the spectrum, and to discover whether further optimization is possible by this process. Optimization was evaluated using receiver operator characteristic (ROC) curves, where special emphasis was placed at the lower false positive values. Over the course of this research, two hypothesis were tested. The first hypothesis conjectures that it is indeed possible to further optimize source detection when using an energy bin other than gross counts. The second hypothesis postulates that if the first hypothesis is true, than there exists a mathematical criterion that predicts this behavior. Both hypothesis were verified to be correct.
Open Access
Dose reconstruction in the large Japanese field mouse using electron paramagnetic resonance spectroscopy of tooth enamel
(Colorado State University. Libraries, 2020) Davis, Mariah, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Gelfand, Martin, committee member
Electron spin resonance (ESR) analysis of tooth enamel is recognized as a reliable method for lifetime dose reconstruction, particularly in human tooth enamel. While the use of ESR to reconstruct dose is well understood for human tooth enamel, the reliability and usefulness of dose reconstruction using ESR in mouse tooth enamel has not been as thoroughly studied. This paper aims to resolve this gap in knowledge concerning the use of the tooth enamel from the Large Japanese Field Mouse as acting dosimeter using EPR spectroscopy. Methods of tooth preparation were analyzed to find a preparation method that resolved a baseline shift or slope in output signals of preliminary samples. Use of purity EDTA (ethylenedinitrilotetraacetic acid, disodium salt dihydrate) was initially found to reduce an observed baseline shift and slope in the output spectrum. Subsequent samples treated with EDTA, however, again saw baseline shifts. More needs to be done to analyze appropriate methodology to reduce the baseline shift, and to further determine the suitability of mouse teeth for ESR spectroscopy for reconstruction of lifetime dose.
Open Access
Electronic dosimeter and thermoluminescent dosimeter correlation study at Catawba Nuclear Station
(Colorado State University. Libraries, 2014) Edquist, Britt Alyssa, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Biedron, Sandra, committee member
Duke Energy's nuclear fleet is comprised of seven nuclear plants. The dosimetry program at every plant includes a comparison of the dose recorded by the TLDs and EPDs at the end of each quarter. EPD over-response is desirable to a degree because the over-response offers a higher dose estimate; however, too great of an over estimate obscures the actual dose a worker receives. An EPD/TLD correlation study was conducted to quantify and identify factors contributing to excess EPD over-response and offer recommendations to improve the EPD/TLD correlation. The EPD/TLD correlations at Catawba Nuclear Station (CNS) (York, SC) were markedly higher than the EPD/TLD correlations at other Duke Energy nuclear plants. The purpose of this study was to investigate the EPD/TLD correlation experienced at CNS. Assemblies, comprised of a phantom (a one gallon plastic jug filled with water) with a V2/V3 Mirion 2000S EPD, V4 Mirion 2000S EPD and TLD inside of a plastic bag that was zip tied to the phantom, were placed in strategic locations within the CNS auxiliary building. Dose rates in the CNS auxiliary building ranged from approximately 10 μSv/h (1 mrem/h) to 350 μSv/h (35 mrem/h). Assemblies were removed after seven days and the dose from the EPDs and TLDs were determined and recorded. Both the V2/V3 and V4 EPDs over-responded compared to the TLD. The V4 over-response was found to be greater than the V2/V3 over-response. Reducing the V4 EPD bias from 15% to 7% would improve the correlation between EPD and TLD doses while still permitting some over-response, allowing for more meaningful EPD dose estimates.
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 member
The 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.
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Laser damage thresholds of ex-vivo pig and rabbit corneas at 2.5 and 2.7 μm with 8 nanosecond laser pulse duration
(Colorado State University. Libraries, 2011) Guo, Yuanqing, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Bernstein, Elliot R., committee member
With the rapid development of advanced laser technology, lasers have been widely applied to research, industry, medicine, military, and consumer products, particularly in the infrared (IR) spectral region. Consequently, safety has been a major concern not only for people who develop and operate lasers, but also for people who use products integrated with lasers. To establish specific laser safety standards for eye protection, many laser safety studies have been conducted for determination of the retina damage threshold in the visible spectral region. The damage threshold for the cornea, a major damage target in the IR wavelength range, however, has not been well established, especially for short laser pulse durations (ns). The purpose of this work was to determine the damage thresholds of the cornea at 2.5 and 2.7 micrometer with 8 ns laser pulses using ex-vivo pig and rabbit eye models. In addition, due to the difference of water absorption coefficients at these two wavelengths (the water absorption coefficient at 2.7 micrometer is about 4-5 times of that at 2.5 micrometer), the role of water absorption for corneal damage was estimated through comparison of damage thresholds at these two wavelengths. Based on our experimental results, both pig and rabbit eyes have similar damage thresholds (ED50) of 0.81 J/cm2 at 2.7 micrometer and 3.66 J/cm2 at 2.5 micrometer. The ratio between the damage thresholds at these two wavelengths is 4.5, which is in good agreement with the ratio of the water absorption coefficients at these two wavelengths. This finding suggests that water absorption in the IR spectral region plays an important role in the damage threshold of the cornea. In addition, temperature changes on the cornea induced by laser energy absorption at varied radiant exposure were monitored through an infrared camera (ThermaCAMTM S65). Results indicate that the increase of temperature on the corneal surface is proportional to the radiant exposure, and with a measured damage threshold of 0.7oC above ambient.
Open Access
Long term stability of sensation thresholds from 10 millisecond pulses of 2.01 micrometer laser light
(Colorado State University. Libraries, 2013) Scott, Ernie, author; Johnson, Thomas, advisor; Brandl, Alex, committee member; Walrond, John, committee member
Current methods for diagnosing and evaluating efficacy for treatment of diabetic neuropathy either give only subjective data or are invasive. However, the use of laser induced sensations to evaluate threshold sensations gives precisely quantifiable and reproducible stimulus and is 100% non-invasive. In this study we evaluated whether or not laser sensation thresholds were stable in 12 human subjects over a four month period of time. Subjects' hands and feet were exposed over eight different exposure sessions to 10 ms pulses of laser light produced by a 50 W Tm: YAG laser system. Sensation threshold values (in mJ/mm2) were determined for each session and compared by regression analysis. The results showed an upward trend in sensation thresholds over time in the majority of the subject's hands and feet, indicating that laser sensation thresholds are not stable over time. Subject desensitization to the sensation over time combined with too short a time between exposures, or variations in baseline skin temperature of the exposure site due to changes in weather are discussed as possible causes of the upward trend. Finally, suggestions are made for future studies to include a study over a longer period of time with more time between exposure sessions and more subjects as well as a study where the exposure sites are heated/cooled to a standardized baseline temperature prior to each exposure session.
Open Access
Long-term hematopoietic response in leukocyte counts and differentials for rhesus macaques (Macaca mulatta) from acute whole-body radiation exposure
(Colorado State University. Libraries, 2023) Chino, Yuiko, author; Johnson, Thomas, advisor; Bailey, Susan, committee member; Kato, Takamitsu, committee member; Walrond, John, committee member
Accumulating evidence from A-bomb survivors and radiation therapy patients suggest that survivors are at risk of developing delayed effects of acute radiation exposure (DEARE). In contrast to acute radiation syndrome (ARS), the underlying mechanisms of DEARE are largely unknown. Better understanding of DEARE is vital for improving estimates of risk and predictions of long-term health outcomes following a variety of radiation exposure scenarios, whether accidental or intentional, and including nuclear accidents, cancer treatment, and space travel. The hematopoietic system is highly sensitive to ionizing radiation (IR) exposure; leukocyte counts reach a nadir in days to several weeks post-acute exposure, followed by a recovery period from 4-8 weeks to a year. Accumulating evidence from the A-bomb survivor cohort and animal studies suggests residual damage in the hematopoietic system persists for a long time. Long-term effects in hematopoietic system are very likely the underlying cause of DEARE disease, although there is limited understanding of the process. In this study, archival leukocyte counts and differentials from the Non-Human Primate Radiation Late Effects Cohort (RLEC), were analyzed to evaluate long-term effects. The RLEC cohort consists of over 200 Rhesus Macaques (Macaca mulatta) previously exposed to acute whole body irradiation from 1.14 to 8.5 Gy and approximately 50 control animals. The dataset was created from blood sampling started approximately 1 year post-exposure and continued every 2-6 months. Linear mixed models were developed for total leukocyte count and the differentials including neutrophil, lymphocyte, and monocyte counts and their percentages. Preliminary analysis was conducted for animals with the same dose level, sex, and age at the time of exposure and age and sex matched control animals. The linear mixed models had statistically significant elevations in leukocyte and neutrophil counts and neutrophil% in irradiated animals compared to the controls. Lymphocyte% was significantly lower in irradiated animals. Longitudinal trends for both control and irradiated animals were consistent with expected trends of aging in hematopoiesis, which is skewed towards production of myeloid lineage cells such as neutrophils and monocytes rather than lymphoid cells. There was no statistical difference among the longitudinal trends of control and irradiated animals. Next analysis was extended from the preliminary analysis with a larger dataset including animals with different dose, sex, age at the time of exposure, as well as mitigator assignment. Longitudinal trends were estimated for different dose levels (control, LD50; 6.8 to 8.5 Gy), and adjusted for sex, age at the time of exposure, and status of mitigator use. All models suggested that dose levels were a statistically significant factor for the longitudinal trends of leukocytes and the differentials. Controls showed a slight decrease of total leukocyte count and monocyte skewed differentiation, consistent with changes estimated from aging in hematopoietic system. The LD50 animals than controls and
Open Access
Occupational dose assessment of 64Cu-ATSM in a veterinary setting
(Colorado State University. Libraries, 2014) Hetrick, Lucas, author; Johnson, Thomas, advisor; Kraft, Susan, committee member; Biller, Barbara, committee member
64Cu-ATSM is an emerging radiopharmaceutical for diagnostic use in Positron Emission Tomography (PET) and has potential utility for radiation therapy but to date there are no studies that assess the occupational doses delivered to workers in either a hospital or veterinary environment. This study consisted of canine patients that were recruited at the Colorado State University James L. Voss Veterinary Teaching Hospital (VTH). The study was aimed at determining the radiation dose to veterinary workers from clinical PET/CT procedures using 64Cu-ATSM. To determine the dose to the workers, each worker was assigned two Electronic Personal Dosimeters (EPDs) to be worn on the chest and waist during the entirety of each procedure. The workers monitored during this study involved included a radiobiologist, a nuclear medicine technician, an anesthesiologist, and a veterinary surgeon. Seven canine patients were imaged over a ten month period with an average mass of 33.7 kg (a range of 20.0 - 55.1 kg) with an average injected activity of 5 MBq kg-1. The dose range for the radiobiologist was 2 -17 µSv, for the nuclear medicine technician 0 -14 µSv, for the anesthesiologist 0 - 12 µSv, and for the surgeon 0 -10 µSv. In a comparison between the results of this study and published literature on occupational exposures from human/veterinary FDG PET/CT procedures, 64Cu-ATSM veterinary PET/CT procedures, on a per patient bias, exposed workers to less radiation.
Open Access
Occupational radiation dose during the trans-catheter aortic valve replacement procedure
(Colorado State University. Libraries, 2015) Shatila, Omar Hani, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Miller, Charles, committee member
Fluoroscopy is an x-ray-imaging technique used during medical procedures such as trans-catheter aortic valve replacement (TAVR). The use of fluoroscopy exposes medical personnel to x-rays scattered from the patient. In this study, radiation dose to personnel at University of Colorado Hospital was measured using Phillips DoseAware dosimeters. The primary physician (0.106 mSv), secondary physician (0.035 mSv), perfusionist (0.027 mSv) received highest median doses of the operating room (OR) personnel. The physicians’ relatively higher doses were expected because of their proximity to the isocenter of the x-ray beam. The perfusionist’s position in the OR, however, is significantly further away from the isocenter than the physicians’ position, suggesting the x-rays scatter unevenly and further away from the isocenter than previously expected. A linear relationship between fluoroscopic output and beam time was not found, however only 21 data points were collected. Factors other than fluoroscopy output can influence dose such as medical personnel movement, beam direction and scatter distribution. A dose map could relate dose to fluoroscopy output without the variability caused by these factors and be a better predictor of medical personnel doses. The dosimeters in this study were susceptible to radio-frequency interference (RF): future studies should consider dosimeters immune to RF.
Open Access
Occupational radiation dose to persons involved in veterinary positron emission tomography
(Colorado State University. Libraries, 2011) Martinez, Nicole, author; Johnson, Thomas, advisor; Kraft, Susan, committee member; Ryan, Stewart, committee member
Several studies have been conducted concerning the dose to hospital personnel from positron emission tomography (PET) radiopharmaceuticals, but to date no specific parallel studies have been done for veterinary PET technologists. Compared to human PET imaging, veterinary personnel are potentially interacting with animal patients for a longer time period, sometimes in close physical proximity, because of the need for anesthetizing patients. There is no equivalent data on personnel exposure from human PET imaging; human patients are not anesthetized and are kept in an isolated room after injection until their imaging procedure. Although veterinary personnel may be interacting more closely with animal patients undergoing PET imaging, radiopharmaceutical doses are generally smaller for animal patients because they weigh less on average. Considering these and other differences between human and veterinary practice, this study aimed to determine, on a per patient basis, the dose to personnel working with PET at Colorado State University's (CSU) James L. Voss Veterinary Teaching Hospital (VTH). Electronic personal dosimeters (EPDs) and supplemental optically stimulated luminescence (OSL) dosimeters were used (in addition to regular dosimetry) to determine radiation doses to veterinary personnel over a period of four months. Participants in the study included nuclear medicine technologists, the on-duty anesthesiology technologist, and occasionally an observer. Individual doses, along with the details of the staff member's activities, were recorded for available personnel for each PET study. Twenty-five scans were conducted over the course of this study: thirteen different dogs, six different cats, and a sheep (with two cats and three dogs having repeat scans). The mass range of the animals was 2.8 to 76.5 kg, with an average of 28.9 kg. The average amount of activity injected was 6 MBq per kg. The dose range for the nuclear medicine technologists was 0 to 30 μSv (7.8 μSv average), for the anesthetist 1 to 22 μSv (8.3 μSv average), and for the observer 0 to 2 μSv (0.4 μSv average).
Open Access
Off site and boundary external radiation exposures from the Cotter Uranium Mill located in Cañon City, Colorado
(Colorado State University. Libraries, 2017) Townsend, Amanda, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Rocca, Jorge, committee member
Although many of the uranium mills in the United States have been decommissioned, the mill tailings remain and can pose health threats to those living nearby. Many studies have been done showing the relationship between radon exposure and lung cancer development for those living near a uranium mill, but it seems that little attention has been paid to the possible threat posed by exposure to gamma radiation from these tailings piles. Since 1979 the Cotter Uranium Mill in Cañon City, Colorado has been measuring external gamma exposure rates at the fence line, and at several offsite locations including the closest residence and the Shadow Hills Golf Course. These exposure rate measurements were tested against background and it has been shown that exposure rates above background exist at all locations except for the nearest residence. Assuming full time occupancy, the excess dose received by members of the public from these exposure rates do not exceed regulatory limits of 100 mrem/yr except at the entrance road of the mill, which was remediated in 2009. For a hypothetical person living in the area of highest exposure rate above background, their risk of developing a fatal cancer is only increased by 0.43%. These exposure rates were compared against the background values measured by the Cotter Corporation and published in their 2010 Environmental and Occupational Performance Report, ALARA Review and Annual Report on Remedial Action Plan Activities. It was later discovered that the background values published in this report were read from a dosimeter that was kept in lead shielding at an offsite location. This means that the background values are only transit values, and are not representative of the actual background. As such, a discussion of what justifies an appropriate background measurement as well as its effect on the results of this study are outlined. Lastly, correlation analysis was performed on the exposure rate data to determine if there was an underlying factor effecting all the exposure rates. It was found that a single factor is responsible for 60.28% of the variation in the exposure rates, but the factor affecting the data could not be determined. It was suspected that either precipitation values, cosmic radiation fluctuations, or radium-226 air concentrations may have affected the exposure rates, and, as such, correlation analysis was conducted. It was determined that no correlation exists between any of these variables and the exposure rates measured. The inability to determine the factor contributing to the fluctuation in exposure rates over the years provides opportunity for continued research.
Open Access
Operational radiation safety considerations during superficial x-ray treatment for veterinary applications
(Colorado State University. Libraries, 2021) Singh, Ashutosh, author; Leary, Del, advisor; Johnson, Thomas, advisor; Wotman, Kathryn, committee member
This study was conducted to determine whether the scatter x-ray emission during a superficial radiation treatment (SRT) using the SRT-100™ result in a significant occupational dose to veterinary personnel present in the room during treatment. Measurements were taken for 50, 70, and 100 kV x-ray for 9 different SRT-100 applicators. The exposure rates at the surface of solid water phantom (SWP) phantom ranged from 3.9 mR/hr for applicator #2 to 396 mR/hr for CB18 for 50 kV, from 41 mR/hr to 2,880 mR/hr for 70 kV, and from 235 mR/hr to 7,500 mR/hr, for 100 kV, respectively. A heat map of scatter x-ray around the x-ray source was generated for 50, 70, and 100 kV at 25 cm and 75 cm above the SWP surface plane. The highest measured exposure rate was at 0.5 m from the applicator and was 76.8 mR/hr at 25 cm above SWP and 33.6 mR/hr at 75 cm above the SWP for 50 kV. Exposure rate values at same locations were 192 mR/hr and 96 mR/hr for 70 kV, and 389 mR/hr and 194 mR/hr for 100 kV, respectively. A horse phantom was utilized to generate a spatial dose profile at 1m for 50, 70, and 100 kV and it was discovered that backscatter emission has an angular response. Residence time for veterinary staff to exceed 10% of quarterly dose limits were calculated for 50, 70, and 100 kV and distances ranging from 0.5m to 2.5 m. These values ranged from a minimum of 24 min for 100 kV at 0.5m to a maximum of 7,813 min for 50 kV at 2.5 m. Minimum distance from the applicator for exposure rates below 2 mR/hr were calculated to be 1.78, 2.52, and 3.45 m, for 50, 70, and 100 kV, respectively.
Open Access
Quantifying biomarkers in wildlife exposed to low doses of environmental radiation pilot study
(Colorado State University. Libraries, 2017) Halim, Nadia, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Lindsay, James, committee member
Exposure of free-ranging wildlife to environmental radiation is of concern following the nuclear accident at the Fukushima-Daiichi facilities in 2011. The uncertainty associated with exposure to chronic ionizing radiation in the vicinity of the accident continues to concern the general population, as well as produce seemingly conflicting scientific results. The risk from prolonged, low dose/low dose rate radiation exposures, specifically to wildlife, remains relatively uncertain. The quantification of chromosomal aberrations such as dicentrics and micronuclei was evaluated as a method of estimating radiation dose to wild boar. Dicentrics and micronuclei found in blood samples of humans are known as a biomarkers of radiation exposure. Blood samples were collected from wild boar in two towns in Fukushima prefecture in Japan and from Kentucky in the USA. External dose was also estimated using soil sample analysis. As a pilot study, only the feasibility of using dicentrics and micronuclei to estimate radiation dose in wild boar was investigated. Additional studies will be required to ascertain the suitability of measuring other chromosomal aberrations and/or decreased telomere length as a method of ascertaining wild boar radiation dose. The hypothesis of the pilot study was that it is possible to estimate chronic radiation dose to wild boar exposed to low levels of lingering environmental ionizing radiation in Fukushima prefecture as well as in irradiated blood from wild boar residing in areas experiencing only natural background radiation with biodosimetry techniques. The data obtained from this investigation do not prove the feasibility of using dicentrics and micronuclei formation to estimate wild boar radiation dose. While the technique for processing wild boar blood in order to observe chromosomal aberrations was successful, the levels of radiation exposure to the wild boar were too low and did not produce biomarkers for use as an indicator of internal radiation dose indicating the hypothesis to be incorrect. Other methods of estimating low radiation dose to wild boar will need to be investigated in future studies.