AbstractThree methods are presented for calculating the multiplication of the delayed-neutron response which occurs in far-subcritical samples of fissionable material irradiated by an external neutron source: a three-energy group analytic expression; the zero prompt-lifetime approximation in conjunction with a one-dimensional steady-state transport theory code; and a three-dimensional time-dependent Monte Carlo code. The accuracy and limitations of the calculational techniques are demonstrated by a comparison with experimental measurements.