Simulation study of cosmic-ray muons for detection of nuclear materials in liquid freight containers

Abstract Accurately detecting nuclear materials concealed within the bulk of cargo containers is essential for establishing a robust defense against nuclear terrorism. Identifying such hidden materials can be achieved through imaging techniques that are ideally non-intrusive—meaning the container does not need to be manually opened—and capable of providing quick and precise identification of the contents. Muon tomography is one such effective imaging technique, utilized across various fields. This technique reconstructs cargo images using cosmic-ray muons, highly penetrative particles that reach the Earth's surface from the upper atmosphere and interact with materials primarily through Coulomb scattering. This study conducts a simulated examination of cosmic-ray muon tomography to detect special nuclear materials, specifically focusing on identifying uranium isotopes U-235 and U-238, as well as plutonium (Pu-239), hidden within large liquid freight containers. A series of muon simulations is performed using the Geant4 software platform to explore the potential for imaging small amounts of concealed nuclear materials within large-scale containers filled individually with water or oil. The results confirm the accurate detection and localization of illicit nuclear content within the substantial volume of liquid freight containers.