Note 1 to entry: Ratio of the total number of neutrons resulting from nuclear fission and a radioactive source, which exist in equilibrium in a subcritical assembly, to the total number of neutrons which would exist in the assembly due to the radioactive source in the absence of nuclear fission.

Note 2 to entry: For critical assemblies this term does not have a useful meaning.

Note 3 to entry: This entry was numbered 393-15-32 in IEC 60050-393:2003.