The Automated Radio-xenon Sampler/Analyzer (ARSA), built by Pacific Northwest National Laboratory (PNNL), can collect and detect several radioxenon isotopes and is used to monitor underground nuclear explosions. The ARSA is very sensitive to 133Xe, 131mXe, 133mXe, and 135Xe (< 1 mBq/SCM) due to the compact high efficiency beta-gamma coincidence detector it uses. For this reason, it is an excellent treaty monitoring system and it can be used as an environmental sampling device as well. Field testing of the system has shown it to be both robust and reliable, but the nuclear detector requires a detailed photomultiplier tube (PMT) gain matching regime that is difficult to implement in a field environment. This complexity is a problem from a maintenance and quality assurance/quality control (QA/QC) standpoint and efforts to reduce these issues have led to development of a simplified beta-gamma coincident detector. The new design reduces the number of PMT’s and, therefore, the complexity of the calibration needed in comparison to the old design. New scintillation materials were investigated and a comparison of three different gamma sensitive well detectors has been completed. In addition, a new plastic-scintillator gas cell was designed that utilized a cell was constructed as well as a newmore » method of forming the scintillator gas cell. The new simplified detector system has compared favorably with the original ARSA design in spectral resolution and efficiency and is significantly easier to set up and calibrate. The new materials and configuration allow the resulting beta-gamma coincendence detector to maintain the overall performance of the ARSA type beta-gamma detector, while simplifying the design.« less