Developing Methods for Measuring the Distribution of Compton Scattered Photons with High-Purity Germanium Detectors Dominic Showalter Project Mentor(s): Michael Braunstein, PhD The purpose of this project was to develop methods to measure the Compton scattering differential cross section using resources available at CWU. When interacting with electrons, the angular distribution of Compton scattered photons is described by the Klein-Nishina cross section. The equation qualitatively shows that for the photon energies relevant to this work, Compton scattered photons are more likely to forward-scatter than they are to back-scatter. We approached measuring this relationship using two High-Purity Germanium (HPGe) detectors. In this experiment the 662 keV gamma rays from a 5 μ Ci sample of Cesium-137 were used as the photon source. To measure data, one detector had a narrow gate set to the energy associated with Compton scattered electrons for a selected scattering angle. The other detector was placed at that scattering angle and measured the coincidence spectrum between itself and the gate detector. Initial analysis of the data showed different results than expected, so further analysis and experimentation is in progress. Presentation Type: Poster Presentation (May 21, 9:30am–3:00pm) Keywords: Compton scattering, Klein-Nishina cross section, gamma spectroscopy SOURCE Form ID: 144 Low Energy Radiation Detection: An Undergraduate Investigation of Radiation Detectors and Modeling ‡ Mason Skeath, Dominic Showalter, James Lewis, Addison Wenger, Erin Craig Project Mentor(s): Mehran Zaini, PhD; Peter Zencak Medical physics relies on accurate radiation detection, so various calibrated radiation detectors and transport simulations have been developed. However, low energy radiation detection remains challenging because of low signal intensity, instrumentation limitations, external source interferences, and signal to noise ratio considerations. To investigate this challenge, we analyzed the interaction of < 20 keV radiation with three detectors: photodiodes, radiochromic film, and perovskite plates. Photodiodes and LD-V1 diagnostic films were placed perpendicular to a 0-5 kV electron beam. We compared the resulting photodiode currents with beam input voltages and Faraday Cup currents. Optical intensity evaluations served as the tool for film response measurements. Monolithic perovskite plates were also developed and then exposed to high-energy X-rays from a medical linac, exempt radioactive sources, and optical photons. Perovskite currents and voltages were measured for optical photons. Furthermore, experiments were translated into the PHITS Monte Carlo package to simulate detector interactions. Photodiodes and film demonstrated minimal response to electron beam radiation. Initial findings suggest that the photodiode window and film thicknesses prevent low energy electron penetration into the active regions of the radiation detectors. Moreover, fluence of exempt radioactive sources seemed inadequate to induce a measurable response in perovskite plates. Nonetheless, perovskite plates showed a verifiable response to optical photons and high energy photons from a medical linac. Based on the sensitivity of the detectors considered, low energy radiation detection likely requires increased energy fluence. Further investigations should explore perovskite response to
radioactive source emissions with alternative instrumentations. Presentation Type: Poster Presentation (May 21, 9:30am–3:00pm) Keywords: Radiation Detection, Medical Physics, Monte Carlo Simulation SOURCE Form ID: 212
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