Theses and Dissertations from UMD
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Item Characterization of the regional, crustal, and global distribution and abundance of the heat producing elements and their geoneutrino flux(2019) Wipperfurth, Scott Alan; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The amount and distribution of radiogenic power generation from the heat producing elements (HPE) U, Th, and K in the Earth is not well constrained. Compositional estimates of these elements vary by a factor of three in the bulk-Earth and 30 in the mantle after removal of the continental crust contribution. Understanding the total power derived from these elements is critical to understanding the power driving the Earth as they supply fuel to the geodynamo and mantle convection. The decay of HPE's produce particles called geoneutrinos and the measurement of the geoneutrino flux reveals the frequency of decay and the abundances of these elements in the Earth. The total geoneutrino flux can be categorized into three major contributors: the dominant component from the nearest 500 km of continental crust surrounding the detector and slightly smaller sub-equal contributions from the remaining global continental crust and the mantle. The negligible amount of HPE's within the core was tested by a mass-balance of the Th/U derived from Pb isotopes (κ_Pb). Each Earth layer was attributed a κ_Pb from representative samples with associated weighting factor from the estimated mass of U in each reservoir. The radiogenic power in the core from U and Th was constrained to ~0.03 terra-watts (median), emphasizing the core's negligible geoneutrino luminosity. To unravel the contribution from the inaccessible mantle to the signal at a detector one must build a physical and chemical description of the local and global crust. The 50x50 km regional geoneutrino flux surrounding the SNO+ detector (Sudbury, Canada) was modeled. 112 geologic samples were analyzed for their U, Th, K abundances and combined with a 3D physical model of the region. To supplement this, the methodology of Huang et al. (2013) was applied to an updated geophysical model for the bulk-crust to predict the global crustal signal at SNO+ and other detectors. Variable correlation is addressed and uncertainties from density, seismic velocity, crustal thickness, and abundances propagated. This dissertation explores the amount and distribution of HPE's within the Earth and their geoneutrino flux through geochemical and geophysical modeling on regional, crustal, and global scales. Together, the results update our understanding of the Earth's geoneutrino flux and the uncertainties still in the system.Item GLOBAL AND REGIONAL REFERENCE MODELS FOR PREDICTING THE GEONEUTRINO FLUX AT SNO+, SUDBURY, CANADA(2013) Huang, Yu; McDonough, William F; Rudnick, Roberta L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Determining the radiogenic heat power that is driving plate tectonics and mantle convection is fundamentally important to understanding the Earth's heat budget and its thermal and chemical evolution. The radiogenic heat power is coupled to the chemical composition of the Bulk Silicate Earth (BSE), which has been debated for decades. Geoneutrinos produced by beta-minus decays in U, Th and K decay systems are correlated to the radiogenic heat power in the Earth. Measured geoneutrino signals at different locations can be used to investigate the distributions and abundances of U and Th, given appropriate reference Earth models. Here I construct both a global and regional scale reference model to predict the geoneutrino signal at the SNO+ detector in Sudbury, Canada. The primary objective of this dissertation is to predict the geoneutrino detection rate for this soon to be operational geoneutrino detector and evaluate its asymmetric uncertainty caused by the log-normal distributions of U and Th in the crust. The focus of both models are on the geoneutrino signal from the continental crust, which determines SNO+'s sensitivity to the mantle geoneutrino signal, which is key to testing different BSE compositional models. The total geoneutrino signal at SNO+ is predicted to be 40 +6 -4 TNU by combining the global and regional reference model predictions and assuming the contribution from continental lithospheric mantle and convecting mantle is 9 TNU. It is not feasible for SNO+, on its own, to provide experimental result that will determine the mantle geoneutrino signal and refine different BSE compositional models because of the large uncertainty associated with the crustal contribution. The regional crust study presented here lowers the uncertainty on the geoneutrino signal that originates from bulk crust when compared to the global reference model prediction ( 30.7 +6.0 -4.2 TNU vs. 34.0 +6.3 -5.7 TNU). A future goal is to increase the resolution of the model in proximal area to the detector (e.g., 50 km by 50 km), which will further reduce the uncertainty. To obtain useful data on the mantle geoneutrino signal, detections of geoneutrinos carried out on the oceans, such as the proposed ocean-bottom Hanohano experiment, will be of significant scientific value.