THU-E - Student Technical Session Thursday 09/24/20 2:00 PM - 4:30 PM
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| Chair(s): Caitlin Condon, Josh Hargraves
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THU-E.1
2:00 PM Using experimental data to inform microdosimetric models for select microorganisms grown in liquid cultures LM Manglass*, Clemson University Department of Environmental Engineering and Earth Sciences
; M Wintenberg, Clemson University, Department of Chemical and Biomolecular Engineering; M Blenner, Clemson University, Department of Chemical and Biomolecular Engineering; nM Martinez, Clemson University Department of Environmental Engineering and Earth Sciences; Li Manglass
Abstract: This work seeks to gain understanding into the dose-response of microorganisms exposed to low levels of radionuclides relevant to anthropogenic nuclear activity for the eventual purpose of developing radio-responsive biosensors; this particular presentation focuses on the determination and development of an appropriate dosimetric model. Two bacteria (P. putida, E. coli) and one yeast (S. cerevisiae) were grown in liquid culture with sources of Pu-239 and Fe-55 added directly to the growth media. The partitioning of radionuclides between the microorganisms and media was found to vary by species and exposure scenario, although in all cases radionuclide concentrations in or on cells was greater than that predicted by cell mass. This implies that radionuclide distribution in the system is not homogenous, necessitating a more thorough examination of dosimetry. To do so, we used microdosimetry techniques within the Geant4/Geant4-DNA software package. Our models consider a variety of targets to reflect current hypotheses regarding the mechanisms of damage from low-dose exposures; while DNA is generally considered to be the primary target for inducing dose related effects, current literature suggests interactions with the cell membrane, proteins, mitochondria, and other organelles may also be responsible for inducing effects as a result of ionizing radiation. Considering a variety of targets is particularly relevant to this work, as some of the bacteria species used are prokaryotic organisms which lack the cell nucleus present in mammalian and other eukaryotic cells (e.g. yeast). We also considered multiple source locations to reflect uptake (inside cells) or sorption (on the cell surface) based on our experimental observations. By considering radionuclide partitioning, microorganism physiology, multiple cellular targets, and multiple source locations, we developed microdosimetry models to more accurately reflect the results of benchtop radionuclide experiments.
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THU-E.2
2:15 PM SAF values for spontaneous fission neutron emitters in the ICRP reference pediatric voxel phantom series KT Griffin*, National Cancer Institute
; KF Eckerman, Oak Ridge National Laboratory; KG Veinot, Y-12 National Security Complex; NE Hertel, Georgia Institute of Technology
Abstract: Purpose: Specific absorbed fraction (SAF) values are a key component in the workflow of internal exposure assessment following inhalation or ingestion of a radionuclide. These SAFs are needed to quickly convert from particle energy released in a source organ to the expected absorbed dose in target organs around the body. For data completeness, SAFs from spontaneous fission neutron emitters are currently needed for the pediatric ages of the ICRP reference phantom series.
Methods: The Monte Carlo code MCNP version 6.2 was used to simulate the Californium-252 (Cf-252) Watt fission neutron spectrum originating from the source regions of a phantom; dose estimation within 43 target organs allowed for assessment of the SAF value for each source-target pair. For ages 0-10, SAFs calculated for the male phantoms were also assigned to the female phantoms, considering their identical anatomy, barring the sex-specific organs. Additionally, chord length distributions were computed for source-target pairs within the pediatric phantom series. These distributions were used in conjunction with a Cf-252 neutron dose point kernel calculated in soft tissue, offering us a reduction in the number of required simulations. The finalized Cf-252 SAF dataset was then extended to other spontaneous fission neutron emitters based on their Watt fission spectrum parameters.
Results: From this work, neutron SAF values for 79 sources and 43 targets were calculated for all 28 radionuclides which decay via spontaneous fission. Chord length distributions compared across the phantom ages help demonstrate the significant effect of inter-organ distance on the differences in estimated internal dosimetry for each phantom.
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THU-E.3
2:30 PM Lysimeter uptake study at Uranium Mine Impacted Sites JT Hargraves*, Oregon State University
; KA Higley, Oregon State University
Abstract: Throughout the duration of the 1950s, uranium mining was prolific throughout the Colorado Plateau. While much of surface mining activity has subsided, there remain large areas with elevated concentrations of uranium and progeny in soils. Cost effective and environmentally benign remediation strategies are desirable over resurfacing and disposal. Techniques such as phytoremediation, or its alternative phytostabilization, are environmentally passive techniques that may provide options for cleanup. As part of an ongoing effort to evaluate the remediation capabilities of endemic plant species, a pilot of phytoremediation, the lysimeter, is utilized to act as a surrogate for field growth in native soil. Candidate species endemic to the region are grown in replicate lysimeters, and leachate analysis by ICP-MS is explored. Lysimeters were constructed for per-plant growth as opposed to deep well trenches, and were utilized in a greenhouse space. Native soil was measured by gamma spectroscopy for radium content by ingrowth of 214Bi and 214Pb progeny, and uranium by Instrumental Neutron Activation Analysis to establish a measure of medium concentration. Replicates are filled with extracted native soil within separate slices of a concentration gradient, allowing for extrapolation of uptake within the gradient. Difficulties in lysimeter construction involving clay content and shrink and swell of soil effect on drainage are discussed, with solutions to artificial drainage proposed.
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THU-E.4
2:45 PM Early DOE worker studies: Obtaining vital status, estimating organ doses, and preliminary results CM Milder*, Vanderbilt University
; BD Ellis, Oak Ridge Associated Universities; MT Mumma, International Epidemiology Institute; AP Golden, Oak Ridge Associated Universities; JD Boice, National Council on Radiation Protection and Measurements; Vanderbilt University
Abstract: The Million Person Study goal of assessing radiation-induced health outcomes in over a million U.S. radiation workers and veterans relies on the availability of robust data sources, including early Department of Energy cohorts from the 1940s-70s. Recent papers have characterized some of these cohorts, and preliminary results are available for several others. Though each cohort is unique, certain challenges appear globally. Accurate dosimetry is vital for constructing dose-response models; rigorous organ dose estimation efforts are crucial prior to analyses. While individual employers collected dosimetric data using film badges, pocket chambers, sporadic bioassay sampling, and area monitoring, challenges persist such as incomplete data, measurement uncertainty, and data recording human errors. Vital status tracing presents a comprehensive challenge. Thus far, at least 88% of traced workers have known vital status; of verified deceased workers, cause of death is known for over 90%. The individual person tracing process is a multi-stage approach in which cohort members are matched to individuals from in-house mortality files, Social Security Administration data, the National Death Index, available state mortality databases, and other online resources. Challenges include incomplete information, registry errors, and name changes. Controlling for confounding is necessary in any epidemiologic study. Early worker studies are necessarily retrospective and rely on contemporaneously recorded data; surrogate covariates must often be used to model expected confounders such as cigarette smoking where valid measures of socioeconomic status become important. Since available surrogates vary by site, further hurdles are expected when combining similar cohorts for added statistical power. In this talk, I will use examples from several early uranium processing cohorts to highlight these key challenges, and I will present preliminary results from the Middlesex Sampling Plant cohort.
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THU-E.
3:00 PM BREAK
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THU-E.5
3:15 PM Understanding the Application of Deep Learning in Gamma Ray Identification ME Gomez Fernandez*, Oregon State University
; KA Higley, Oregon State University; A Tokuhiro, University of Ontario Institute of Technology
Abstract: Known as the fourth industrial revolution, digitization is an ongoing trend in all fields in which various industries are now leveraging to develop new technologies in support of their businesses. The nuclear industry is beginning to understand the use of machine learning methods and their potential to revolutionize some aspects of nuclear safety and radiation detection. Gamma-ray spectroscopy is a mature area of radiation protection that has multiple applications and has been a candidate application for neural networks with the focus to automate isotope identification by using raw information. While many deep learning structures have been proposed, it has been shown in practice that these are prone to learn characteristics that are not descriptive or relevant. Therefore, this presentation will focus on understanding the uses and limitations of convolutional neural networks (CNNs) to the application of gamma-ray identification. It will present the mechanism of a CNN as applied to isotope identification, the reasoning behind the deep learning algorithm classification, and future challenges.
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THU-E.6
3:30 PM Temporal Change and Ecological Half-lives of Cs-137 Concentration in a Forest-stream Ecosystem After Fukushima Daiichi Nuclear Power Plant Accident Y Chino*, Colorado State University
; T Gomi, Tokyo University of Agriculture and Technology; Y Oyama, Tokyo University of Agriculture and Technology; E Haque, Jahangirnagar University; TE Johnson, Colorado State University
Abstract: Nine years have passed since the nuclear power plant accident at Fukushima Daiichi nuclear power plant, but there still much radioactive cesium (Cs-137) remains in forest environments. Given that around 70% of the contaminated area is covered by forest, understanding the fate of Cs-137 in forest ecosystem is indispensable for people working in forests and living in the vicinity of the area as well as the use of forest products. In manufactured cedar forests, which is one of the major types of forests in Fukushima, it is found that Cs-137 migrates within the ecosystem through the linkage of stream and riparian ecosystems via food web from cedar litter to fish species. Whereas the Cs-137 contamination is strongly related to both of the stream and riparian forest ecosystems, most of the previous studies focused on one ecosystem or some specific ecosystem components. In this study, we examined temporal change of Cs-137 concentration of cedar litter from forest floor and stream, surface soil, POM (particulate organic matter), terrestrial and aquatic insects, and white spotted char (Salvelinus leucomaenis) based on the results of field samplings conducted in a headwater forest-stream ecosystem at Towa-region in Fukushima for four seasons in 2012-13 and 2016-17. The Cs-137 concentration of all samples significantly decreased between the two sampling periods. We also calculated ecological half-lives (Teco), which are an indicator of the rate of contamination change with time including various environmental processes. The calculated Tecos were 1.6-7.2 years with the shortest of cedar litter from forest floor and the longest of FPOM (fine particulate organic matter). Tecos in aquatic components were larger than terrestrial components. It was estimated that Cs-137 contamination in stream ecosystems decreased more slowly than riparian systems since newly supplied litter, less and less contaminated with time, was the only source of contamination in riparian systems, while fallen litter as well as resuspension of sediment and POM kept the contamination in the stream ecosystem. Also, Tecos of soil, litter, and white spotted char were in the range of previous studies for Fukushima and other sites. As indicated in previous studies, we need to expect slower decreasing rate of 137Cs represented by longer ecological half-lives in the future.
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THU-E.7
3:45 PM Indoor Radon measurements at the University of Utah U Gella*, Alcorn State University
; M Beitollahi, University of Utah; E Divver, Utah Department of Environmental Quality; F Monnette, University of Utah; J Billa, Alcorn State University; S Adzanu, Alcorn State University; M Shelly, University of Utah
Abstract: Indoor Radon measurements were conducted at the University of Utah (U of U), using passive procedures namely: Charcoal canister for the short term & Alpha Track for long term study. In the first phase of this study, a total of 136 short-term radon kits were installed in 35 buildings across the U of U campus in basement, first, and second floors. Testing locations were selected randomly among old and new structures considering residents of the buildings. In the preliminary phase, average Radon concentration was 0.70 pCi/L with a maximum of 3.3 pCi/L and a minimum of 0.3 pCi/L. Ten samples (~7%) out of 136 were shown above the EPA’s national average of 1.3 pCi/L. A gamma dose rate was also measured using ion-chamber to find correlation between Radon concentrations and gamma exposure in each individual location. Both radon and gamma exposure rates followed the same trend from highest in the basements to lowest in the upper levels.
In the second phase of this study, a total of 87 long-term radon test kits (Alpha Track), were installed in 44 buildings on basements and first floors, the minimum time required for these kits to be exposed is 91 days. The partial conclusion of this study in relation to short-term testing is to recommend the above 10 locations to retest in 1-2 years to check if there is an increase in radon concentration levels. The final results of this study will be presented and discussed in this paper.
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THU-E.8
4:00 PM Impact of combined phosphorus-32 and synthetic estrogen (17-α ethinylestradiol) exposure on Arabidopsis thaliana seed growth C Vogel*, Clemson University
; L Manglass, Clemson University; P Zou, Clemson University; C Eiman, Clemson University; N Martinez, Clemson University
Abstract: Ecotoxicological studies traditionally determine or model effects resulting from single pollutants, yet no environmental contaminant is ever truly the sole toxicant in a contamination scenario. Although mixture studies have increased recently, very few include radiological contaminants. Moreover, there has been further interest in developing and promoting a holistic approach to risk assessment for both humanity and the environment. In this vein, our work aims to improve knowledge on combined contaminant effects by examining the influence of two contaminants potentially found in wastewater effluent on seed development of the model plant Arabidopsis thaliana. Batch experiments as root length assays were conducted for 10 days on agar plates with varying concentrations of phosophorus-32 and the synthetic estrogen (17-α ethinylestradiol, EE2). A total of nine treatments (five individual and four combined exposure scenarios) plus one control treatment were made with three plates per treatment and 10 seeds per plate. EE2 was incorporated into growth media at a range of environmentally relevant concentrations (1.5, 5, 10, and 20 ng L-1), and phosphorus-32 (t1/2 = 14.3 days) was incorporated at 0.07 µCi g-1 agar (~10 mGy d-1). Endpoints assessed include root length, rosette development, and germination rate. The results of this study suggest that the introduction of EE2 into growth media induces early germination and faster root growth in A. thaliana seeds, where the addition of phosphorus-32 may have a synergistic effect that amplifies the impact on root length.
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