What happens when a neutron strikes a uranium-235 nucleus?

When a slow neutron strikes a uranium-235 nucleus, it induces nuclear fission, causing the nucleus to split into two smaller fragments. Each of these fragments contains approximately half the protons and neutrons of the original nucleus.1

This process results in the release of a significant amount of thermal energy, gamma rays, and two or more additional neutrons. Because the binding energy per nucleon increases when the heavy uranium nucleus splits into smaller, more stable nuclei, energy is liberated in the process.12

Under specific conditions, the neutrons released during this fission can strike and split surrounding uranium-235 nuclei, emitting even more neutrons and creating a self-sustaining chain reaction. In a nuclear reactor, this reaction is maintained at a controlled level, whereas in an atomic bomb, the reaction multiplies rapidly to release a massive amount of energy.1