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.
The symbols are defined as:[3] The multiplication factor, k, is defined as (see Nuclear chain reaction): In an infinite medium, neutrons cannot leak out of the system and the multiplication factor becomes the infinite multiplication factor,
k =
k
, which is approximated by the four-factor formula.