Critical mass

Critical mass is the minimum quantity of fissile material that can sustain a nuclear chain reaction under specified conditions. Its value depends on the material’s composition, shape, density, and surroundings.

Nuclear chain reaction: A sequence in which neutrons from one nuclear reaction trigger further nuclear reactions. Critical mass marks the conditions under which fission-generated neutrons can maintain this sequence.
Fissile material: Material whose nuclei can undergo fission after absorbing neutrons and can support a chain reaction. Critical mass applies to fissile material, whose composition determines its neutron behavior.
Nuclear reactor: A system that controls a sustained nuclear chain reaction to produce heat or neutron radiation. Reactors are designed to maintain controlled criticality while managing neutron production and loss.
Criticality safety: The prevention of unintended nuclear chain reactions during the handling, storage, and processing of fissile materials. It manages configurations and operations rather than treating critical mass as a fixed standalone number.
Neutron: A subatomic particle with no electric charge, found in atomic nuclei and released in many fission reactions. Neutrons trigger fission and can escape the material, determining whether multiplication continues.
Nuclear fission: The splitting of an atomic nucleus into lighter nuclei, often releasing neutrons and energy. Fission supplies the neutrons whose continued production defines criticality.
Nuclear reactor core: The part of a nuclear reactor containing fuel and the components that control or moderate neutron behavior. Core geometry and materials determine the conditions for critical operation.
Critical size: The dimensions at which a fissile system becomes critical under specified material and environmental conditions. Critical size emphasizes geometry, while critical mass expresses the corresponding quantity of material.
Neutron multiplication factor: The ratio of neutron populations in successive generations of a nuclear chain reaction. A factor of one corresponds to a self-sustaining, critical chain reaction.
Criticality: The condition in which a nuclear chain reaction’s neutron population remains steady from one generation to the next. Critical mass is the material quantity associated with reaching this condition in a specified setup.

Linked from 10 pages