Air Cargo Scanning
Schematic of Air Cargo Scanner showing X-ray (yellow) and Neutron (green)
scanning points as cargo is passed through the scanner
Neutrons are produced by some particular, neutrons are very sensitive to ray scanner. The intrinsic efficiency of the
radioisotope sources, by large particle organic materials including foodstuffs, neutron radiography process means that
accelerators and most conveniently by plastics, narcotics and explosives. The cargo is also exposed to very little radiation
commercial, sealed-tube electronic approach leads to a large improvement in – equivalent to the level that would be
generators. These generators have the simplicity, ease-of-use and scanning time. received naturally during two hours of
advantage of being easy to operate and Deploying a neutron-based screening flying – and there is no measureable
produce no radiation when turned off. solution in an airport environment involves activation of the cargo after scanning.
The most common contraband detection several challenges. Cargo scanning must also fit in with
approach using neutrons has been to try Radiation safety concerns are clearly existing handling procedures with minimal
and measure the characteristic high- high on the list of system operators and disruption to freight flow around an airport.
energy radiation called gamma-rays that freight handlers (and their customers) This implies that the scanning process itself
are produced when neutrons interact with whose cargo is being scanned. The system must be quick, that the scan results are
matter. This approach is highly specific, must be designed to meet stringent rapidly available and that the operators have
targeting individual substances on the radiation safety criteria, so that operators the necessary tools to make quick decisions
basis of their elemental composition. are exposed to no more radiation than they as to whether a particular cargo should be
However, the processes involved in the would be working around a conventional X- passed or subjected to further inspection.
production and detection of the gamma-
rays are very inefficient. This leads to the
need for intense neutron sources, large
and expensive detector systems and long
scan times. Imaging is also quite
complicated, making it difficult to separate
the signature of a concealed threat
material hidden inside a much larger
cargo. These factors have limited the
uptake of neutron-based approaches in
airports.
An alternative approach has been
developed by the Commonwealth Scientific
and Industrial Research Organisation
(CSIRO) in Australia. The approach uses
neutrons directly to form a transmission
radiographic image, just as X-rays are used
in a conventional screening system.
Because neutrons interact with matter in a
complementary way to X-rays, by
combining radiographic images obtained
using X-ray and neutron sources it is
possible to infer a lot of information about Scan of cargo containing assorted items (from left – computer equipment,
the composition of cargo being scanned. In machinery, foodstuffs and office items
20 April 2008 Aviationsecurityinternational
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