Handheld device for simultaneous monitoring of fast neutrons and gamma rays

Currently at the INEEL, a handheld device is being developed to measure fast neutrons and gamma rays using a single detector instead of a previous two detector system. The handheld detection system presented here uses a single 1/2 inch (diameter) by 1/2 inch (long) liquid scintillator detector (BC501). This means the detection system can be made smaller, lighter, less expensive, and is expected to be more sensitive than the original system. A smaller and lighter device makes it possible to be used in several applications such as customs inspection, border security, environmental radiation monitoring, and so on. 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 here, charge integration and crossover timing. Figures of merit were calculated for both methods for a threshold energy range of 50 to 600 keV. Results show that the crossover method gives much better PSD for electron energy of 100 keV and lower, whereas the charge integration method leads to better separation above 100 keV. However, the neutrons and gamma rays are totally separated for energies of 100 keV and above in both techniques. We are currently designing a miniaturized electronic system to be incorporated in the handheld device.