Monte Carlo Analysis Of An Organic Glass Beta Cell For Radioxenon Detection

Detection of radioactive xenon in atmospheric samples is the only technology in the International Monitoring System that can unambiguously identify a detected event as nuclear. Currently deployed systems use beta-gamma coincidence detection to identify the various xenon isotopes in atmospheric gas samples. These systems use plastic scintillator to detect the beta particles and sodium iodide to detect the correlated X-rays and gamma rays. The plastic scintillator has hollow, cylindrical cell geometry with the atmospheric sample inside to create a near-4-pi detection geometry. One limitation of plastic scintillator is the so-called “memory effect”, whereby radioactive xenon diffuses into the plastic during the measurement; this effect raises the background for subsequent measurements. Stilbene organic scintillator has been previously explored to mitigate the memory effect but suffers from machining difficulty due to its brittle nature. Here, we explore an organic glass scintillator that was recently develop by Sandia National Laboratories as an alternative material for the organic beta detection cell. This material has improved brightness compared to plastic and stilbene and is very easy to machine. The glass can be easily melted in a laboratory can cast into various shapes using custom molds. An MCNP model has been developed of a radioxenon detection system based on organic glass and sodium iodide. This model will be used to conduct a simulation study to characterize the detection sensitivity compared to a traditional plastic beta cell.