Akeh neutron sane kalebang nyabran nucleus sane terus melah nucleus tiosan kawedangan pinaka K. Nilai K agengan saking 1 suksmannyane inggih punika reaksi fisi ngelebang sayan akeh neutron yaning saihang sareng sane kaisep, taler punika sane kawedarang pinaka reaksi berantai mandiri.
The average number of neutrons released per nucleus that go on to fission another nucleus is referred to as k. Values of k larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self-sustaining chain reaction.