A well-type NaI(Tl)/BC404 phoswich detector for atmospheric radioxenon monitoring

The monitoring of radioxenon in the atmosphere is one of several methods to detect nuclear weapon tests as part of the Comprehensive Nuclear Test Ban Treaty. For ultra-low radioxenon detection, a phoswich detector with two scintillators coupled to a single photomultiplier was explored to simplify the time-based coincidence detection systems such as SAUNA and ARSA. We present a well-type NaI(Tl)/BC404 phoswich detector, newly developed by the Institute of Nuclear Physics and Chemistry, which consist of a thin BC404 cell to detect beta and conversion electrons, and a NaI(Tl) crystal to detect X-rays and gamma-rays. Moreover, the pulses of the detector were sampled and processed at 1GS/s with 10-bit ADC by a high-speed digitizer. In the preliminary experiments with various sources, the detector was test to have comparable sensitivity with the existing detectors in energy resolution, detection efficiency, background, memory effect and MDCs. The gamma resolution achieved 6.9% at 662keV. The coincidence efficiency of 133Xe at 81keV region is about 71% while gas loss in the stainless tube and the valve was accounted. In addition, the MDC of 133Xe was calculated by 0.2mBq/m3 under current gas process capability.