The photofission reaction against the illicit transport of nuclear material in cargo containers: A review on recent achievements and future challenges in active photon interrogation

X-ray scanning is widely used by customs for visual inspection of cargo containers at border controls. When Special Nuclear Material (SNM) such as uranium or plutonium is suspected, an active non-destructive nuclear measurement method serves as a second-line tool. The photofission reaction, central to the Active Photon Interrogation (API) technique, enables the direct detection of SNM. This paper reviews European advances in API over the past decade through three Horizon 2020 projects. In C-BORD (2015–2018), Europe’s first photofission system was tested at the Maasvlakte terminal of the Port of Rotterdam (Netherlands), with experiments on depleted uranium and container mock-ups demonstrating integration into a stationary 9 MeV industrial X-ray scanning facility. The ENTRANCE project (2020–2023) evaluated a mobile 7 MeV X-ray scanner at the Škrljevo terminal of the Port of Rijeka (Croatia), investigating the 5–6 MeV actinide photofission threshold and assessing operational performance. The MULTISCAN 3D project (2021–2025) explored new approaches using high-energy photons from laser–plasma sources. Collectively, these developments have strengthened nuclear security and enhanced Europe’s capacity to counter illicit SNM trafficking.