subcritical mass

In physics, a subcritical mass refers to an amount of fissile material that is less than the critical mass. This means it is insufficient to sustain a nuclear chain reaction. The critical mass is the minimum amount of fissile material needed for a self-sustaining fission chain reaction. Factors influencing critical mass include the type, density, purity of the material, and the surrounding system's geometry and neutron reflection. A spherical shape minimizes critical mass due to its optimal volume-to-surface ratio, reducing neutron escape. Safety systems in nuclear reactors, such as safety rods, are designed to quickly bring the reactor to a subcritical state to prevent a runaway reaction.1234