Electron accelerator options for photo-detection of fissile materials

For national security, it is important to detect the presence of special nuclear materials, especially highly-enriched uranium (HEU). Generally used methods for such detection include interrogation by photons and neutrons. For example, photofission in HEU can be initiated with 14-MeV photons. The resulting delayed neutrons and photons from the fission fragments are clear signatures of the presence of HEU. One can generate high- energy photons using electron accelerators via various mechanisms. In this paper, we will describe two of them, namely electron bremsstrahlung and Compton backscattered photons. We focus on these two mechanisms because they cover a wide range of accelerator requirements. Electron bremsstrahlung can be generated using a compact low-energy electron linac while the generation of Compton backscattered photons requires a high-energy electron accelerator of a few hundred MeV. We review these two options, describe their accelerator requirements, and compare their relative merits.