Real-time radioxenon measurement using a Compton-suppressed well-type phoswich detector for nuclear explosion monitoring

Graduation date: 2014Radioxenon detection is a technique used to monitor nuclear explosion and verify the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Because of an ultra-low concentration of radioxenon at radioxenon monitoring stations, radioxenon detection systems must have high sensitivity. This sensitivity is measured in terms of detector's minimum detectable concentration (MDC). It is required that radioxenon monitoring systems should have a MDC of less than or equal to 1 mBq/m³ for ¹³³Xe. A Well-type Actively Shielded Phoswich Detector (WASPD) for radioxenon detection was designed and assembled at the Radiation Detection and Dosimetry lab at Oregon State University. The active shielding mechanism is integrated into the phoswich detector to improve the MDC of the radioxenon by reducing unwanted background events. Anode pulses were processed using a user programmable digital pulse processor. All digital processing functions were implemented in a FPGA device in real-time. The detector was characterized for different radioxenon isotopes. MDC calculation of the detector showed that the results are close or below 1 mBq/m³ for all radioxenon isotopes