 The neutron multiplicity is the average number of neutrons
produced by fission of a particular nuclide, v.
 The multiplication factor is defined as the ratio of the neutron
concentration in one generation to that of the preceding generation; the
symbol k is used.
 An assembly of fissionable materials is said to be critical, when, on
average, exactly one of the several neutrons emitted in the fission
process causes another nucleus to fission. Criticality thus depends on the
geometrical factors as well as the distribution and kinds of material
present.
 If N_{i} thermal neutrons are present in a system, their
absorption will result in a certain number N_{i+1}
of next
generation thermal neutrons.
 k_{eff},
'k_{effective}' is a practical
k for a real
finite detector
k_{¥}, 'k_{infinity}' is a
more theoretical concept which assumes that there is no leakage of
neutrons from the system, i.e. the reactor is infinitely large.
 k_{eff}
< 1 Þ subcritical
k_{eff}
= 1 Þ critical
k_{eff}
> 1 Þ supercritical
The effective multiplication factor is defined as
k_{eff}
= N_{i+1} / N_{i+1}

