[en] Potential diversion of nuclear materials is a major international concern. Fissile (e.g., U, Pu) and other nuclear materials (e.g., D, Be) can be detected using 6-7 MeV gamma rays produced in the ¹⁹F(p,αγ)¹⁶O reaction. These gamma rays will induce neutron emission via the photoneutron and photofission processes in nuclear materials. However, they are not energetic enough to generate significant numbers of neutrons from most common benign materials, thereby reducing the false alarm rate. Neutrons are counted using an array of BF3 counters in a polyethylene moderator. Experiments have shown a strong increase in neutron count rates for depleted uranium, Be, D₂O, and ⁶Li, and little or no increase for other materials (e.g., H₂O, SS, Cu, Al, C, ⁷Li). Gamma source measurements using solid targets of CaF₂ and MgF₂ and a SF₆ gas target show that proton accelerator of 3 MeV and 10-100 microampere average current could lead to acceptable detection sensitivity