Optimizing the signal-to-noise ratio for the PELAN system

Pulsed elemental analysis with neutrons is a portable system for the detection of explosives, weighing less than 45 kg. It is based on the principle that explosives and other contraband contain various chemical elements such as H, C, N, O, etc. in quantities and ratios that differentiate them from other innocuous substances. Neutrons are produced with a pulsed 14 MeV (d-T) neutron generator. Separate gamma-ray spectra from fast neutron, thermal neutron and activation reactions are accumulated and analyzed to determine elemental content. Currently, a 7.6 cm×7.6 cm BGO detector is incorporated into the design. However, the high γ-ray efficiency of this detector has a drawback in that it detects γ-rays from the environment surrounding the object under interrogation. These γ-rays from the environment are essentially noise that must be filtered from the signal from the object under interrogation. Since there is no practical way to focus the neutrons, the signal-to-noise ratio of the detector must be modified. In the past 2 years, we have tried several approaches to solve this problem.