User:Ntouran/Four factor formula

The four-factor formula is used in nuclear engineering to determine the multiplication of a nuclear chain reaction in an infinite medium. The formula is $$k_{\infty} = \eta f p \epsilon$$

Multiplication
The multiplication factor, k, is defined as $$k = \frac{\mbox{number of neutrons in one generation}}{\mbox{number of neutrons in preceding generation}}$$

If k is greater than 1, the chain reaction is supercritical, and the neutron population will grow exponentially.

If k is less than 1, the chain reaction is subcritical, and the neutron population will exponentially decay.

If k = 1, the chain reaction is critical and the neutron population will remain constant.

In an infinite medium, neutrons cannot leak out of the system and the multiplication becomes the infinite multiplication, $$k = k_{\infty}$$, which is given by the four-factor formula.