Chain reaction

Definition

A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In nuclear chemistry, it often refers to fission reactions where neutrons released trigger further fissions.

5 Must Know Facts For Your Next Test

1. In a nuclear fission chain reaction, a single neutron initiates the splitting of heavy nuclei like Uranium-235, releasing additional neutrons.
2. Sustaining a chain reaction requires a critical mass of fissile material to ensure that enough neutrons cause further fission events.
3. Chain reactions can be controlled (as in reactors) or uncontrolled (as in nuclear explosions).
4. The concept of neutron multiplication factor (k) is crucial; if k=1, the reaction is self-sustaining, k>1 leads to an exponential increase, and k<1 causes the reaction to die out.
5. Moderators are substances used in reactors to slow down neutrons, making them more likely to induce further fissions.

Review Questions

• What role do neutrons play in a nuclear fission chain reaction?
• How does the neutron multiplication factor (k) affect the behavior of a chain reaction?
• Why are moderators important in sustaining a controlled chain reaction?

Related terms

Critical Mass:

The minimum amount of fissile material needed to maintain a self-sustaining nuclear chain reaction.

Neutron Moderator: A substance used in nuclear reactors to slow down fast neutrons, increasing the likelihood of further fission.

Fissile Material: Material capable of sustaining a nuclear fission chain reaction with thermal neutrons.