What role do neutrons play in nuclear fission?

In the context of a fission device like an atomic bomb, neutrons are the fundamental agents that initiate and sustain the nuclear fission process.12

Their role can be summarized as follows:

• Initiation: Fission begins when a neutron strikes the nucleus of a fissile atom, such as uranium-235. This collision provides the necessary excitation energy for the heavy nucleus to overcome its fission barrier and split into two smaller fragments.34
• Propagation: The fission of a single nucleus releases a significant amount of energy along with two or more additional neutrons. These "daughter" neutrons are then available to strike other surrounding fissile nuclei, triggering further fission events.351
• Chain Reaction: When the number of neutrons produced is sufficient to induce subsequent fissions, a chain reaction is established. In an atomic bomb, the configuration is designed to be supercritical, meaning the number of fissions multiplies rapidly at each step, releasing a massive, explosive amount of energy in a fraction of a second.251

Essentially, neutrons act as both the trigger and the carrier that allows the energy-releasing reaction to propagate through the material.16