Fissionable materials are distinguished from other high-effective atomic number materials by producing dual-energy x-ray radiation sufficient to cause fission in fissionable materials and directing the dual-energy x-ray radiation sufficient to cause fission in fissionable materials towards a physical region. X-ray radiation and a product of fission from the physical region are sensed. An absorption of the dual-energy x-ray radiation by the physical region is determined based on the sensed x-ray radiation, and whether the physical region includes fissionable material is determined based on the presence of a product of fission.