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Pacific Northwest National Laboratory uses beta-gamma coincidence detectors in a number of xenon sampling and measurement systems to enable simultaneous, sensitive measurements of 131Xe, 133Xe, 133mXe, and 135Xe for treaty monitoring applications. In recent years, a new style of beta–gamma detector was developed to improve upon the detector module used in the Automated Radioxenon Sampler/Analyzer. The results of an MCNP5 Monte Carlo simulation of the new detector cell are presented, with particular emphasis on the identification of an energy deposition sequence with the potential to introduce significant error into the detector efficiency calibration. This sequence occurs when an 81 keV gamma from 133Xe is absorbed in an inactive region of the CsI(Na) scintillator, followed by emission of a 31 keV X-ray from cesium (or possibly a 28.5 keV X-ray from iodine). These X-rays add excess counts into the 31 keV peak observed in the decay of 133Xe. The impact of this effect on different efficiency calibration techniques is discussed. [ABSTRACT FROM AUTHOR]

The development of portable nuclear instrumentation demands compact high sensitivity detectors operated at room temperature. The sensitivity of these detectors mainly depends on two parameters: absolute efficiency and energy resolution. In order to provide high efficiency, large volumes are needed. For semiconductor detectors able to operate at room temperature, the largest effective volumes with acceptable resolution are achieved with CdZnTe coplanar-grid and pixel detectors. On the other hand, new scintillation materials were recently developed with spectrometric capabilities only reachable some years ago with semiconductors. In this work we compare the performance of two state of the art detectors of different technologies with a relative large volume: a coplanar-grid CdZnTe detector with dimensions 15 mm × 15 mm × 10 mm and a LaBr3 (Ce) crystal with volume 18 mm × 18 mm × 30 mm. The CdZnTe crystal was made by Yinnel Tech (USA) and the detector was manufactured by BSI (Latvia). The LaBr3 (Ce) scintillator was grown and encapsulated by Saint-Gobain (France). The energy resolution for the CZT detector is 2.05% FWHM at 662 keV. The resolution for the scintillator at this energy was near 3 %. The total efficiency was studied in a setup with calibrated point sources. The experimental spectra were compared with Monte-Carlo simulations performed with Geant4. The implications of the results of this comparison are discussed in the context of the practical use of these units. [ABSTRACT FROM AUTHOR]