Development of a handheld device for simultaneous monitoring of fast neutrons and gamma rays

Currently at the Idaho National Engineering and Environmental Laboratory, a handheld device is being developed to measure fast neutrons and gamma rays using a single detector. The handheld detection system presented uses a single 12.7 mm (diameter) by 12.7 mm (length) liquid scintillator detector (BC501). The detection system can be made small and light. A small and light device can be used in several applications such as customs inspection, border security, and environmental radiation monitoring. The use of only one detector requires that the neutrons and gamma rays be distinguished by the shape of their pulses in the detector. Two methods of pulse shape discrimination (PSD) are presented: charge integration and zero crossing. Figures of merit were calculated for both methods for a threshold energy range of 50-600 keVee. Results show that the zero crossing method gives much better PSD for 100 keVee and lower, whereas the charge integration method leads. to better separation above 100 keVee. However, the neutrons and gamma rays are totally separated for energies of 100 keVee and above in both techniques. We are currently designing a miniaturized electronic system to be incorporated into the handheld device.