Reduction of delayed-neutron contribution to variance-to-mean ratio by application of difference filter technique

The difference-filtering correlation analysis was applied to time-sequence neutron count data measured in a slightly subcritical assembly, where the F eynman-a analysis suffered from large contribution of delayed neutron to th e variance-to-mean ratio of counts. The prompt-neutron decay constant infer red from the present filtering analysis agreed very closely with that by pu lsed neutron experiment, and no dependence on the gate-time range specified could be observed. The Ist-order filtering was sufficient for the reductio n of the delayed-neutron contribution. While the conventional method requir es a choice of analysis formula appropriate to a gate-time range, the prese nt method is applicable to a wide variety of gate-time ranges.