Accelerating fissile material detection with a neutron source
View Patent ↗A neutron detector system for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly to count neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source. The system includes a Poisson neutron generator for in-beam interrogation of a possible fissile neutron source and a DC power supply that exhibits electrical ripple on the order of less than one part per million. Certain voltage multiplier circuits, such as Cockroft-Walton voltage multipliers, are used to enhance the effective of series resistor-inductor circuits components to reduce the ripple associated with traditional AC rectified, high voltage DC power supplies.
1. A system for characterizing a radiation source as fissile material or non-fissile material, comprising:
a neutron generator configured to irradiate the radiation source by inducing radiation in the radiation source;
a detector configured to receive and count neutrons emitted from the radiation source; and
an analyzer component coupled to the detector and configured to determine the number of times that a group of n simultaneously emitted neutrons is observed from the radiation source after a defined measurement time period is repeated a defined number of times to derive a neutron count measurement, subtract an expected number of pairs of neutrons emitted by a hypothetical non-fission Poisson neutron source embodied in the neutron generator during the measurement time period from the number of pairs of observed neutrons derived from the neutron count measurement, produce a histogram representing the number of times different group sizes occur from a number of measurement time periods, derive a Poisson count distribution for the Poisson neutron source, overlay the histogram and the Poisson count distribution to provide a visual indication of the difference in correlation of emitted neutrons from the radiation source, and determine if the number of pairs of observed neutrons exceeds the expected number of pairs of neutrons in at least a portion of the overlay of the histogram and Poisson count distribution in order to characterize the radiation source as fissile material if the observed number exceeds the expected number, or as non-fissile material if not.
2. The system of claim 1 further comprising a DC (direct current) power supply coupled to the neutron generator, the power supply comprising:
an AC (alternating current) receiving circuit;
a pair of rectifiers converting the input AC signal to respective DC output signals;
a summer circuit receiving the respective DC output signals and configured to add the respective DC output signals together such that electrical ripple present on a DC output signal from one rectifier of the pair of rectifiers is added 180 degrees out-of-phase to the electrical ripple present on a DC output signal from the second rectifier of the pair of rectifiers; and
a Cockroft-Walton voltage multiplier circuit coupled to the summer circuit and configured to increase the output of the summed DC output signals to a desired DC voltage level.
3. The system of claim 2 wherein the defined measurement time period is ½ msec., and wherein a fissile source creates real correlations between emitted neutrons, and a non-fissile source creates no correlation or only accidental correlations between emitted neutrons.
4. A method characterizing a radiation source as fissile material or non-fissile material, comprising the steps of:
irradiating the radiation source by inducing radiation in the radiation source using a neutron generator;
receiving and counting neutrons emitted from the radiation source in a detector circuit placed proximate the neutron source;
determining the number of times that a group of n simultaneously emitted neutrons is observed from the radiation source after a defined 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 embodied in the neutron generator during the measurement time period from the number of pairs of observed neutrons derived from the neutron count measurement;
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 in correlation of emitted neutrons from the radiation source, for the purpose of distinguishing fissile material from non-fissile material;
determining if the number of pairs of observed neutrons exceeds the expected number of pairs of neutrons in at least a portion of the overlay of the histogram and Poisson count distribution in order to characterize the radiation source as fissile material if the observed number exceeds the expected number, or as non-fissile material if not.
5. The method of claim 4 further comprising:
receiving an AC (alternating current) receiving circuit in a power supply circuit coupled to the neutron generator;
converting the input AC signal to respective DC output signals in a pair of rectifiers;
summing the respective DC output signals from the pair of rectifiers together such that electrical ripple present on a DC output signal from one rectifier of the pair of rectifiers is added 180 degrees out-of-phase to the electrical ripple present on a DC output signal from the second rectifier of the pair of rectifiers; and
multiplying the output of the summed DC output signals in a Cockroft-Walton voltage multiplier circuit coupled to increase the output of the summed DC output signals to a desired DC voltage level.