GLOBAL AND REGIONAL REFERENCE MODELS FOR PREDICTING THE GEONEUTRINO FLUX AT SNO+, SUDBURY, CANADA

Abstract

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.