Which nuclide is included in Fissile Material set?

• A. Uranium-233
• B. Uranium-238
• C. Neptunium-237
• D. Thorium-232

Answer: (A)

Fissile materials are those that can sustain a nuclear chain reaction with slow (thermal) neutrons. They have a favorable fission cross-section for these neutrons and can release enough neutrons to keep the reaction going. Among the listed nuclides, Uranium-233 is fissile because it readily fissions when struck by thermal neutrons and can maintain a chain reaction. Uranium-238 is not fissile by itself; it’s fertile, meaning it can capture a neutron and eventually become fissile Pu-239 under the right conditions, but it cannot sustain a chain reaction on its own. Neptunium-237 is not used as a primary fissile material for sustaining thermal neutron chains. Thorium-232 is fertile as well, becoming Uranium-233 after neutron capture and decay, but it cannot sustain a chain reaction by itself. So Uranium-233 fits the fissile material set.