Detecting special nuclear materials in suspect containers using high-energy gamma rays emitted by fission products
AssigneeThe Regents of the University of California
InventorsEric B. Norman, Stanley G. Prussin
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Abstract
A method and a system for detecting the presence of special nuclear materials in a suspect container. The system and its method include irradiating the suspect container with a beam of neutrons, so as to induce a thermal fission in a portion of the special nuclear materials, detecting the gamma rays that are emitted from the fission products formed by the thermal fission, to produce a detector signal, comparing the detector signal with a threshold value to form a comparison, and detecting the presence of the special nuclear materials using the comparison.
Claims6
A method of interrogating a container, comprising the steps of:
- a) irradiating the container for approximately 30 seconds with neutrons having energies between about 2.45 and 14 MeV or with a gamma ray beam having an energy of at least 10 MeV;
- b) stopping the irradiating;
- c) after stopping the irradiating, counting β-delayed gamma rays having an energy range between about 3 and 6 MeV for approximately 30 seconds;
- d) making a first plot comprising number of β-delayed gamma rays counted in step c as a function of β-delayed gamma ray energy to produce an observed energy spectrum;
- e) making a second plot of the total number of β-delayed gamma rays counted in a portion of the energy range between about 4 and 6 MeV as a function of time in order to determine an effective half-life;
- f) comparing the observed energy spectrum with known energy spectra produced by fission products of U-235;
- and
- g) concluding that there is U-235 in the container when:
- the observed energy spectrum and the known energy spectra have the same overall shape;
- and
- the observed effective half-life is approximately 20 to 30 seconds.
Dependencies are inferred from the claim text.