Critical mass

Definition

Critical mass is the minimum amount of fissile material needed to maintain a self-sustaining nuclear chain reaction. It is essential for the functionality of nuclear reactors and atomic bombs.

5 Must Know Facts For Your Next Test

1. Critical mass depends on factors such as the type of fissile material, its purity, shape, and density.
2. For uranium-235, the critical mass is approximately 52 kg in a spherical shape.
3. A neutron reflector can reduce the required critical mass by reflecting escaping neutrons back into the fissile material.
4. Supercritical mass occurs when there is more than enough fissile material to sustain an exponential increase in reactions, leading to an explosion if uncontrolled.
5. Subcritical mass refers to a quantity of fissile material that cannot sustain a chain reaction.

Review Questions

• What factors influence the critical mass of a fissile material?
• How does a neutron reflector affect the critical mass?
• Differentiate between subcritical, critical, and supercritical masses.

Related terms

Fission:

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

Chain Reaction: A series of nuclear fissions where released neutrons from one fission cause further fissions in other nuclei.

Neutron Reflector: A material that reflects escaping neutrons back into the fissile core to reduce the amount needed to achieve criticality.