Criticality

Definition

Criticality refers to the state of a nuclear chain reaction when it becomes self-sustaining. It is a crucial concept in controlling nuclear reactors and ensuring safety in medical applications of nuclear physics.

5 Must Know Facts For Your Next Test

1. A system is considered critical when each fission event causes exactly one subsequent fission event.
2. Supercriticality occurs when more than one fission event results from each original event, leading to an exponential increase in reactions.
3. Subcriticality occurs when fewer than one fission event results from each original event, causing the reaction to die out.
4. Achieving and maintaining criticality is essential for the stable operation of nuclear reactors used in medical isotope production.
5. Control rods are used in reactors to absorb neutrons and manage the rate of the chain reaction, thus maintaining criticality.

Review Questions

• What does it mean for a nuclear reactor to be in a critical state?
• How do control rods help maintain criticality within a reactor?
• What are the differences between subcritical, critical, and supercritical states?

Related terms

Fission: The process by which a nucleus splits into two or more smaller nuclei, along with the release of energy.

Neutron Moderator: A material that slows down fast neutrons, making them more likely to cause further fission events.

Chain Reaction: A series of reactions where a reactive product or by-product causes additional reactions to take place.