A 24-element Silicon PIN Diode Detector for High Resolution Radioxenon Measurements using Simultaneous X-ray and Electron Spectroscopy

The measurement of atmospheric radioxenon is an important tool for monitoring nuclear weapons testing. The development of new and improved xenon detection methods supports the monitoring program of the Comprehensive Test Ban Treaty Organization (CTBTO). In the current work we have developed a 24-element Si PIN diode detector to measure both the characteristic X-rays and the high energy mono-energetic conversion electrons emitted by the xenon radioisotopes. The low noise properties and ultra-thin entrance window of the PIN diodes are well suited for resolving the relatively low energy X-ray lines while simultaneously measuring the high energy conversion electrons with high collection efficiency and near-Gaussian peak shapes. The use of coincidence gating between the X-rays and conversion electrons can further improve the detection sensitivity, which we show to rival the current HPGe and scintillator based xenon detection systems that rely mostly on Gamma-ray and Beta/Gamma coincidence detection, respectively. The Si PIN detector arrangement offers others advantages compared to current xenon detection methods, such as compact construction, intrinsically low background, and the lack of any memory effect from previous measurements. We discuss the construction of the detector and present measurements performed with 131mXe, 133Xe, 133m Xe and 135Xe. Finally, we make an estimate of the minimum detectable concentration (MDC) for each isotope and compare with the CTBTO requirements.