Critical Mass
| Formula / Notation | m_crit = π²D/(νΣ_f) for sphere; depends on geometry and material |
|---|---|
| Also Known As | Criticality mass, fissile critical mass, supercritical/subcritical mass |
What is Critical Mass?
Critical mass is the minimum mass of fissile material (such as uranium-235 or plutonium-239) needed to sustain a self-propagating nuclear chain reaction. If the mass is below critical, too many neutrons escape without causing fission and the chain reaction dies out. At or above critical mass, the chain reaction becomes self-sustaining or explosive (supercritical). It depends on geometry, density, and purity.
Formula & Notation
Other Names / Synonyms: Criticality mass, fissile critical mass, supercritical/subcritical mass
Properties & Characteristics
Uses & Applications
Safety Information
Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.
Key Facts
Frequently Asked Questions
Critical mass is the minimum mass of fissile material (such as uranium-235 or plutonium-239) needed to sustain a self-propagating nuclear chain reaction. If the mass is below critical, too many neutrons escape without causing fission and the chain reaction dies out. At or above critical mass, the chain reaction becomes self-sustaining or explosive (supercritical). It depends on geometry, density, and purity.
Critical mass calculations are fundamental to nuclear weapons design, nuclear reactor physics, and criticality safety in nuclear fuel processing facilities. Subcritical masses are maintained in all fuel storage and reprocessing to prevent accidental criticality.
Accidental criticality (e.g., Tokaimura accident, 1999) releases intense gamma and neutron radiation, causing acute radiation syndrome and potentially death. Strict criticality safety rules (mass limits, geometry controls, neutron absorbers) govern all handling of fissile materials.
The formula or notation for Critical Mass is: m_crit = π²D/(νΣ_f) for sphere; depends on geometry and material