Master of Science (MS)
Physics and Astronomy
Purpose: The purpose of this work was to test the feasibility of using a silicon on insulator microdosimeter, which mimics the size and shape of particular cells within the human body, to determine dose equivalent from a 239PuBe neutron source with uncertainty less than 10%. Methods: A batch of microdosimeters were analyzed in terms of their physical surface conditions and basic diode characteristics such as leakage current as a function of bias voltage, to select those with the best performance. A calibration protocol was developed utilizing an 241Am alpha particle source and a reference tail pulse generator. Neutron spectra were acquired using two different converter layers placed atop the microdosimeter: a tissue-substitute converter made from high-density polyethylene, and a boron converter consisting of epoxy coated with boron powder. To compare the experimental results, a Monte Carlo code was written to simulate the alpha particle and neutron irradiations. Dose equivalent was determined using an average quality factor calculated for each spectrum on the basis of the ICRU definition (1986). Results: Using the tissue-substitute converter, the cell-shaped microdosimeters were able to determine dose equivalent with uncertainty less than 10%. However, uncertainties were 13.5% when using the boron converter. Conclusion: The cell-shaped silicon on insulator microdosimeters proved feasible for further research and development. With higher quality silicon chips, this type of microdosimeter could become a simple, small, and lightweight device to determine dose equivalent in real-time and to provide improved radiation protection for radiotherapy patients and personnel who are occupationally exposed to radiation.
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Mazza, Anthony P., "The Development of a Novel Silicon on Insulator Microdosimeter with Sensitive Volumes Modeled after Living Cells" (2014). LSU Master's Theses. 4270.
Vassiliev, Oleg N