Mobile neutron resonance transmission analysis (NRTA) systems offer the promise of portable, on-site identification of special nuclear material, but their performance is often hindered by background signals that obscure true neutron time-of-flight (TOF) information. Center for Nuclear Security Science and Policy Initiatives (NSSPI) student Seungwoo Son’s master’s research investigated ways to address this challenge by developing a simulation-driven approach to reduce random and false coincidences in a mobile NRTA setup. His thesis work applied detailed Monte Carlo modeling to evaluate how detector design choices, shielding materials, and neutron source characteristics influence system performance.
Working under the guidance of Dr. Farheen Naqvi, NSSPI Faculty Fellow and Instructional Assistant Professor in the Department of Nuclear Engineering, Son used the Geant4 simulation toolkit to quantify the origins of background coincidences and propose design modifications that significantly improve TOF resolution. His work demonstrated that reducing the neutron source activity and optimizing shielding, for example, by replacing outer polyethylene with borated polyethylene, can meaningfully lower random coincidence rates. He also investigated gamma-neutron misidentification in the GS20 detector and showed that maintaining a 5-mm detector thickness strikes an effective balance between neutron efficiency and false coincidence reduction. Further simulations and experimental validation could be necessary to demonstrate the effectiveness of the proposed modifications.
According to Son, the findings of his research “provide inputs for modifying and improving the current isotopic mobile NRTA setup that has potential application in the on-site verification of special nuclear material.” This could lead to cost-effective and easily implementable pathways to enhancing isotope identification in mobile NRTA systems.
Son completed his Master’s of Science degree in Nuclear Engineering with a specialization in nuclear nonproliferation at Texas A&M University in the Summer of 2025. During his time at NSSPI, he engaged fully in the program’s academic and professional development opportunities while balancing the responsibilities of his graduate fellowship through the Republic of Korea Army. In 2024, Son presented his NRTA research at a poster session at the Institute of Nuclear Materials Management (INMM) Annual Meeting and received the student poster award for the Nonproliferation and Arms Control Division. He has since returned to South Korea to continue his career as a captain in the South Korean military.