Date of Award

Summer 8-31-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Mathematics and Natural Sciences

Committee Chair

Dr. Christopher B. Winstead

Committee Chair School

Mathematics and Natural Sciences

Committee Member 2

Dr. Khin Maung Maung

Committee Member 2 School

Mathematics and Natural Sciences

Committee Member 3

Dr. Michael D. Vera

Committee Member 3 School

Mathematics and Natural Sciences

Committee Member 4

Dr. Jeremy Scott

Committee Member 4 School

Mathematics and Natural Sciences

Abstract

This research is focused on the development of a computational model which will calculate the effects of radiation on the chemical composition of the atmosphere. The approach utilizes the open-source chemical kinetics toolkit Cantera to model the creation of radiation-induced reactant species within irradiated air mixtures. Chemical solutions are iteratively stepped toward chemical equilibrium within a ‘constantly stirred’ (homogeneous) reactor of fixed volume. Three different radiation chemistry models are implemented in several different pulsed and continuous radiation schemes. The first model includes the mechanisms and rates of a pulse radiation model from the literature to test the validity of the new approach by comparison. The second uses identical mechanisms with the latest accepted rates to explore the change in induced chemical product yields in both schemes. The third model implements an extensive list of reactions and rates found within atmospheric chemistry literature and is an attempt to posit an updated radiation chemistry model that fits both pulsed and continuous radiation models and experimental data from the literature.

Measurements of radiation-induced ozone within continuously irradiated air mixtures demonstrated a need for a more accurate representation of the energy deposition distribution specific to the radioactive source. The volume in the space above the source is partitioned into a grid of independent voxels, and an energy deposition rate at each location is calculated. The average dose rate along the optical path of the spectroscopy-based model validation experiment is calculated from the voxel data. This method offers the flexibility necessary to easily correlate precomputed solutions with experimental measurements made through any part of the irradiated air mixture.

Several computational solutions are computed for dry 80/20 nitrogen/oxygen gas mixtures at various pressures with a gaseous mix of reactants introduced at different rates corresponding to a range of dose rates. Yields produced by the new approach in the pulse radiation scheme are found to be in good agreement with experimental results within the literature. Spectroscopy measurements of radiation-induced ozone show a strong correlation with computational results of the posited model in the continuous radiation scheme at the average dose rate of the optical measurements.

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