Semester of Graduation

Spring 2019

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

Iodine-131 (I-131) is a major fission product among other radionuclides released during a nuclear incident. This radioiodine has a half-life of 8.02 days and the primary organ of uptake through ingestion or inhalation is the thyroid gland. For these reasons, nuclear power plants must routinely monitor I-131 through air sampling. Currently, there are two adsorbing media to collect I-131: activated charcoal and silver zeolite cartridges. Silver zeolite cartridges are generally used during a post nuclear incident due to its affinity for iodine while not adsorbing noble gases such as krypton-85 and xenon-135. After an air sample is taken from a plume, the cartridge is taken to a low radiation background area for measuring the radioactivity of I-131. This is usually done by using a γ-spectroscopy detection system. To use these detectors, the system must be calibrated using the same source geometry as in the field. Source geometry refers to source to detector orientation when counting. Because of licensing issues, radiation protection problems, and financial concerns, many agencies or institutions use a single barium-133 (Ba-133) sealed point source on top of a silver zeolite cartridge as their calibration standard for air sampling purposes. This method does not reflect the actual gaseous I-131 distribution in the silver zeolite cartridge. Consequently, the ambient gaseous I-131 activity would be underestimated due to different source geometries/counting efficiencies. This study compares various geometrical arrangements of both Ba-133 and I-131 spiked filter media in a silver zeolite cartridge to mimic the gaseous I-131 distribution found in the field in order to establish conversion factors back to a Ba-133 sealed point source geometry for proper calibration of a sodium iodide detection system based on their counting efficiencies. The results of this study demonstrate that nine is the best correction factor for estimating I-131 activity measured in the field using a Ba-133 sealed point source for calibration.

Committee Chair

Wang, Wei-Hsung

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