GAMMA RAY DETECTION IN CARGO Jackson Choate Cargo
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GAMMA RAY DETECTION IN CARGO Jackson Choate
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
Gamma-Ray Radiography • Gamma ray scanners can penetrate denser materials than conventional x-rays • Cobalt-60 produces 1. 25 Me. V 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
High Energy X-Ray Radiography • High Energy X-rays can be produced through Bremsstrahlung process • Electrons used are accelerated up to 6 Me. V, 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
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
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
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 3 He or BF 3 (using 10 B), to emit ionized particles n + 3 He → 3 H + p + en + 10 B → 7 Li + α + 2 e. However, these detectors can only count the number of neutron interactions, not their energies
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
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/technicalpublications/Documents /3310854. pdf. Retrieved Oct. 2010.
