CAFNA(R) Coded Aperture Fast Neutron Analysis for contraband detection: preliminary results

We have developed a near field coded aperture imaging system for use with fast neutron techniques as a tool for the detection of contraband and hidden explosives through nuclear elemental analysis. The technique relies on the prompt gamma rays produced by fast neutron interactions with the object being examined. The position of the nuclear elements is determined by the location of the gamma emitters. For existing fast neutron techniques, in Pulsed Fast Neutron Analysis (PFNA), neutrons are used with very low efficiency; in Fast Neutron Analysis (FNA), the sensitivity for detection of the signature gamma rays is very low. For the Coded Aperture Fast Neutron Analysis (CAFNA(R)) we have developed, the efficiency for both using the probing fast neutrons and detecting the prompt gamma rays is high. Compared to PFNA, the improvement for neutron utilization is n², where the total number of voxels in the object being examined is n³. Compared to FNA, the improvement for gamma-ray imaging is proportional to the total open area of the coded aperture plane; a typical value is n²/2, where n² is the number of total detector resolution elements or the number of pixels in an object layer. We have performed analysis, Monte Carlo simulations, and preliminary experiments using low and high energy gamma-ray sources. The results show that a high sensitivity 3-D contraband imaging and detection system can be realized by using CAFNA