System Modeling and Design Optimization for a Next-Generation Unattended Sensor

We are developing a next-generation unattended sensor that can detect and identify radiation sources while operating on battery power for several weeks. The system achieves smaller size and weight over systems that use NaI:Tl and ³He detectors by using a relatively new scintillator, Cs₂LiYCl₆:Ce (CLYC). This material can detect both gamma rays and thermal neutrons, has best-case energy resolution under 4% full width at half maximum at 662 keV, and allows for particle discrimination by pulse amplitude as well as pulse shape. The overall design features an array of sixteen CLYC detectors, each read out by a photomultiplier tube and custom pulse processing electronics. A field-programmable gate array analyzes the energy spectra using computationally efficient algorithms for anomaly detection and basic isotope identification. In this paper, we report the results of a modeling study to optimize various parameters of the unattended sensor for best performance. Key parameters include the number and placement of detectors, dimensions and weight of the moderator, and location of the batteries. These results have guided the design of the proof-of-concept prototype.