Gamma Ray detection in cargo

1
Gamma Ray detection in cargo

• Jackson Choate

2
Cargo Scanning

• Thousands of cargo containers enter ports each
  day
• Every minute inspecting a cargo container keeps
  it from shipping
• Advances in gamma ray, high energy x-ray, and
  neutron scanning are reducing inspection times

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Gamma-Ray Radiography

• Gamma ray scanners can penetrate denser materials
  than conventional x-rays
• Cobalt-60 produces 1.25 MeV gamma rays capable
  of penetrating 15 18 cm of steel
• Provides an x-ray of cargo containers
• Gamma ray detectors can also pick up photon
  emissions from radioactive sources, but some may
  be benign, i.e. Potassium-40

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High Energy X-Ray Radiography

• High Energy X-rays can be produced through
  Bremsstrahlung process
• Electrons used are accelerated up to 6 MeV,
  producing x-rays capable of penetrating 30 40
  cm of steel
• Penetrate deeper than radioactive gamma rays, but
  are more expensive to use
• Deliver about 1000 times more radiation to
  stowaways

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Neutron Interrogation

• Inelastic neutron scattering produces gamma rays
  with distinctive energies
• Neutrons generated by pulsed fusions of deuterium
  and tritium
• Gamma ray energies can be compared to those of
  known materials
• Does not provide an image, but photon spectrum
  provides more information about what materials
  are present

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High Energy Photon Detection

• To create an image, photons must be correlated to
  their origin via a collimator made of a dense
  material
• Collimated photons then hit a scintillator,
  emitting a lower energy photon
• The lower energy photon can then be detected via
  a photomultiplier

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Neutron Detection

• Neutrons can be detected through scintillation as
  well, but are more commonly detected through
  absorption reactions
• Gas proportional detectors use gases with high
  neutron absorption cross-sections, such as 3He or
  BF3 (using 10B), to emit ionized particles
• n 3He ? 3H p e-
• n 10B ? 7Li a 2e-
• However, these detectors can only count the
  number of neutron interactions, not their energies

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Conclusion

• High energy particles and radiation can be used
  to minimize the amount of time it takes to
  inspect cargo
• Gamma rays and high energy x-rays provide a
  thorough image of target
• Neutrons provide a photon spectrum that can be
  compared to known materials

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Sources

• Clements, Elizabeth. "High-energy X-rays search
  containers." Symmetry Aug 2010 n. pag. Web. Oct
  2010.
• Gilmore G, Hemingway J. Practical Gamma-Ray
  Spectrometry. John Wiley Sons, Chichester
  1995.
• Jones,J. L. Haskell, K. J. Hoggan, J. M.
  Norman, D. R. (June 2002) (PDF). ARACOR
  Eagle-Matched Operations and Neutron Detector
  Performance Tests. Idaho National Engineering and
  Environmental Laboratory. http//www.inl.gov/techn
  icalpublications/Documents/3310854.pdf. Retrieved
  Oct. 2010.