Time correlation analysis of neutron detection is routinely applied in the quantitative determination of spontaneously fissioning isotopes, especially plutonium. Since these materials are usually also fissionable by the neutrons emitted, multiplication must be taken into account. A method is presented that allows calculation of the effect on characteristic parameters of the assay. These are the factorial moments of the probability distribution of the multiplicities of the neutrons emitted. The results can be written as analytic functions of the fission probability. They are given for the case of an energy spectrum common to all types of neutrons and for cases in which the source spectrum influences the probability of fission or the efficiency of detection.
