Development of Beta-gamma Phoswich Detection System for Operational Intervention Level Monitoring in Radiation Emergency Situations

Abstract

In the event of a radiological disaster, response actions for individuals are determined based on radiation monitoring results. The International Atomic Energy Agency (IAEA) has provided guidelines for the development and application of Operational Intervention Levels (OILs) for reactor emergencies. OILs serve as critical benchmarks for implementing protective measures in nuclear and radiological emergencies, ensuring rapid responses based on measurable and easily interpretable data. This dissertation focuses on the development of detection systems applicable to OIL determination. A beta- gamma Phoswich detector based on GAGG(Ce) and BC-404 plastic scintillators was designed to be applicable to key monitoring categories, including surface monitoring, skin monitoring, and thyroid monitoring. To optimize the Phoswich detector, the thickness of the BC-404 plastic scintillator was determined using Geant4 Monte Carlo simulations, and foundational studies were conducted using point sources and BC-404 scintillators of various thicknesses for verification. Pulse shape discrimination technology was utilized to separate radiation signals from the two scintillators, and the figure of merit was evaluated to confirm proper signal separation. Performance evaluations of the developed Phoswich detection system were conducted for beta and gamma radiation under OIL scenarios, providing detection efficiencies. Additionally, dose conversion coefficients were derived to facilitate practical implementation. The ability to perform measurements under various scenario conditions with a single detector is expected to enhance its versatility and practical applicability.