An Overview of Radiography with Emphasis on Dual Energy for Cargo Inspection
H. E. Martz, Jr., S. Glenn, J. Smith, C. Divin
Lawrence Livermore National Laboratory, Livermore, California, U.S.A.
X-ray radiography plays a key role in the inspection of cargo entering the U.S. via sea and land ports. This talk will provide an overview of the different sources, detectors, and configurations that have been deployed or are being considered for cargo inspection. Sources include radioisotopes as well as bremsstrahlung and quasi-monochromatic accelerator-based generators. Detectors include scintillators, such as cadmium tungstate and Cerenkov detectors coupled to photodiodes or photomultiplier systems. System configurations include single- and dual-energy systems deployed as mobile or fixed units.
X-ray dual-energy radiography can potentially meet an important objective in cargo inspection by revealing the presence of high-atomic number materials via differences in transmission at differing x-ray energies. However, the use of traditional bremsstrahlung sources has shown limited sensitivity in achieving material discrimination due to overlap and similarity between the broad-band high- and low-energy spectra. This problem is exacerbated in highly-attenuating cargo.
Recent work in the development of monoenergetic photon sources promises a potential alternative. These sources can provide highly-collimated, monoenergetic, x-ray pencil beams, resulting in better separation of the high- and low-energy spectra and likely better image contrast. Our calculation-based comparison of bremsstrahlung and monoenergetic dual-energy radiographic technologies shows that the mono-energetic sources should achieve better material discrimination and may provide an important adjunct and a potential alternative to traditional dual-energy bremsstrahlung sources.
This work has been supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under IAA HSHQDC-12-X-00341. This support does not constitute an express or implied endorsement on the part of the Government. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.