RADIOXENON MEASUREMENTS WITH THE PHOSWATCH DETECTOR SYSTEM

Many of the radioxenon detector systems used in the International Monitoring System and in other applications employ beta/gamma coincidence detection to achieve high sensitivity. In these systems, the coincidence detection is implemented by requiring simultaneous signals from separate beta and gamma detectors. While very sensitive to small amounts of radioxenon, this approach requires careful calibration and gain matching of several detectors and photomultiplier tubes. An alternative approach is the use of a phoswich detector in which beta-gamma coincidences are detected by pulse shape analysis. The phoswich requires only a single photomultiplier tube and thus is easier to set up and calibrate, and can be assembled into a more compact and robust system. In the past, we have developed a COTS detector system, named PhosWatch, which consists of a CsI(Tl)/BC-404 phoswich detector, digital readout electronics, and on-board software to perform the pulse shape analysis. Several units of this system have been manufactured and are now evaluated at several radioxenon research laboratories. In this paper, we will report results from production tests and some of the evaluations, including a side-by-side comparison of a SAUNA detector and a PhosWatch system using atmospheric radioxenon samples. In addition, we will show initial results obtained withmore » a higher speed version of the readout electronics, digitizing at 500 MHz and thus able to better resolve the fast pulses from the BC-404.« less