Nuclear Fission and Chain Reactions
Nuclear fission is the splitting of a heavy atomic nucleus into smaller fragments, releasing enormous amounts of energy and neutrons that can sustain a chain reaction.
What You Need to Know
Key Concept Diagram
Fission occurs when a heavy nucleus (e.g. U-235) absorbs a neutron and splits into two daughter nuclei
Each fission event releases 2–3 neutrons that can trigger further fission — this is a chain reaction
Critical mass is the minimum amount of fissile material needed to sustain a self-propagating chain reaction
Nuclear reactors use control rods to absorb excess neutrons and regulate the reaction rate
Key Vocabulary
Fission
The splitting of a heavy atomic nucleus into two smaller nuclei, releasing energy and additional neutrons
Chain Reaction
A self-sustaining sequence of fission events in which neutrons from each reaction trigger further reactions
Critical Mass
The minimum quantity of fissile material required to sustain a nuclear chain reaction
Control Rod
A neutron-absorbing material inserted into a reactor core to regulate the rate of the chain reaction
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
What initiates a fission reaction in uranium-235?
Question 2
Why are control rods used in nuclear reactors?
Question 3
What is critical mass in nuclear physics?
Key Concepts Summary
- ●Fission occurs when a heavy nucleus (e.g. U-235) absorbs a neutron and splits into two daughter nuclei
- ●Each fission event releases 2–3 neutrons that can trigger further fission — this is a chain reaction
- ●Critical mass is the minimum amount of fissile material needed to sustain a self-propagating chain reaction
- ●Nuclear reactors use control rods to absorb excess neutrons and regulate the reaction rate