Patent ID: 8891720

Claim:
A method of determining whether a radiation source has the characteristic of fission, comprising the steps of: counting neutrons emitted from the radiation source; defining a measurement time period; determining the number of times that a group of n simultaneously emitted neutrons is observed from the radiation source after the measurement time period is repeated a defined number of times to derive a neutron count measurement; subtracting an expected number of pairs of neutrons emitted by a hypothetical non-fission Poisson neutron source during the measurement time period from the number of pairs of observed neutrons derived from the neutron count measurement to provide a calculated result; determining if the number of pairs of observed neutrons exceeds the expected number of pairs of neutrons by a defined error range for each subtraction of the expected number of pairs of neutrons from the observed number of pairs of neutrons, wherein the defined error range represents a statistical measure that is indicative of fission by the observed neutrons; producing a histogram representing the number of times different group sizes occur from a number of measurement time periods; deriving a Poisson count distribution for the Poisson neutron source; and overlaying the histogram and the Poisson count distribution to provide a visual indication of the difference provided by the calculated result, wherein a difference between the number of pairs of observed neutrons and the expected number of pairs of neutrons in excess of the defined error range in at least a portion of the overlaid histogram and Poisson count distribution characterizes the radiation source as fissile.