Four factor formula
The four-factor formula, also known as Fermi's four factor formula is used in nuclear engineering to determine the multiplication of a nuclear chain reaction in an infinite medium.
| Symbol | Name | Meaning | Formula |
| Reproduction Factor | |||
| The thermal utilization factor | |||
| The resonance escape probability | |||
| The fast fission factor |
The six factor formula defines each of these terms in much more detail.
Multiplication
The multiplication factor,, is defined as :- If is greater than 1, the chain reaction is supercritical, and the neutron population will grow exponentially.
- If is less than 1, the chain reaction is subcritical, and the neutron population will exponentially decay.
- If, the chain reaction is critical and the neutron population will remain constant.