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US Seaports: Finding the Needle in Hundreds of Haystacks
by Winn Hardin, Contributing Editor - AIA Posted 06/28/2004
Just after September 11th, the U.S. inspected about 2 percent of the 5.7 million cargo containers that pass through the US each year, with only 30 percent of those containing material that matches the cargo manifest. Since then, new federal guidelines mandating random inspections and certain port pilot projects around the world have increased the inspection rate to between 5 and 10 percent. Spreading 5.7 million containers around the US’ 365 river and seaports – not including border crossings – illustrates the US' exposure to cargo-based threats.
‘‘The current maritime [cargo container] screening technologies are made for [detecting] contraband, but at best, they detect explosives with an extremely high error rate upwards of 30 percent,’‘ said Dan Inbar, chairman of Homeland Security Research Corp. (HSRC, San Jose, CA), ‘‘and images these systems show are extremely complex to read.’‘
Today, the big questions lying before cargo inspection are not whether the systems should be deployed – educated sources concur that such measures are critical to border safety -- but which technologies, where and when.
Gamma systems offer promise
Cargo imaging inspection systems fall into two main categories: gamma ray and x-ray. X-ray systems use lower power tube sources (less than 1 MeV) and high-energy linear accelerators (1 MeV and above). Gamma ray systems use radioactive isotopes or pulsed fast neutron (PFN) sources to show structural information inside the container as well as the elemental make up of materials inside. Gamma ray systems, although less developed than x-ray systems, can also detect nuclear materials – a differentiation that x-ray systems alone cannot make.
Science Applications International Corp. (SAIC, San Diego, CA) offers a highly mobile, less expensive system that uses Cesium 137 or Cobalt 60 radioactive isotopes to generate gamma rays. These gamma rays penetrate the cargo container and are collected by special arrays of highly sensitive photo multiplier tubes, rather than arrays of photodiodes as the x-ray systems do. The photo multiplier tubes are larger, and so the spatial resolution is reduced, from a maximum of 9 mm for the gamma ray system compared to around 2 mm for x-ray systems. Based on their energy levels, gamma rays penetrate approximately 6.25’‘ of steel compared to up to 12 inches for high-energy x-ray systems. Greater penetration can translate to faster scans of approximately 1 foot per second for high-energy x-ray systems at maximum resolution compared to 1 inch per second for SAIC’s relocatable isotope-based gamma ray systems
Despite slower throughputs, SAIC’s isotope based systems require a fraction of the shielding necessary to protect operators from high-energy, linear accelerator based x-ray systems. Cargo inspection systems operating at 6 MeV and above require many tons of shielding, which can increase system costs by a factor of two or more and preclude relocatable systems capable of highway driving. Another advantage of isotope over x-ray is that an isotope source is a constant source of radiation, while linear accelerators are pulsed. Constant wave sources do not require synchronizing the accelerator, detector and cargo, which simplifies the electronics.
OSI Systems Inc (Hawthorne,CA) offers another type of gamma ray imaging system acquired through a recent acquisition of Ancore Corp (Santa Clara, CA). OSI’s pulsed fast neutron analysis (PFNA) uses a pair of orthogonal pulsed neutron sources to create a 3D scan of a cargo container. The scan contains 3D structural information in addition to chemical composition of objects within the cargo container. This functionality does not come cheap, however. Reported estimates put a PFNA system at between $10 and $15 million (US), compared to $5 million for a 3 MeV mobile system or less than $2 million for a mobile isotope based system. Higher power x-ray based systems fall between the $5 million and $10 million level depending on the power levels, single or dual x-ray sources and other considerations.
X-ray inspection: a versatile technology
Initially exploited for medical imaging and then expanded to luggage inspection and non-destructive testing systems in electronics among other industries, x-ray systems and sources have benefited from years of development. As one would expect, development leads to product segmentation; as always, the trick is matching the system to the application.
‘‘One mega-electron volt is pretty much the cutoff for X-ray tubes,’‘ said John Avolio, director of cargo, aviation and government affairs at L3 Communications (New York City). ‘‘Anything above that uses a linear accelerator.’‘ L3 offers several systems using x ray tubes, including a 160 keV, 320 keV and 450 keV. Avolio claims the 450 keV system delivers 4 inches of steel penetration. To put that in perspective, most intermodal cargo containers are made 1/8’‘ steel, so 4’‘ would seem more than adequate for any inspection – but is that the case?
‘‘The answer to the question, what is the minimum power for cargo inspection is, ‘it depends,’’‘ said vice president of business development, Dan Bundy at Bio-Imaging Research Inc. (BIR, Lincolnshire, IL), a vendor of high-power x-ray inspection systems. ‘‘Checking empty containers to make sure they are indeed empty before returning them is a good application for lower energy systems. You don’t need high energy to see that…In the case of our systems, where the content is varied and densely packed, you really need – in our opinion – a floor of 6 MeV.’‘
In addition to fixed cargo inspection facilities already installed in Japan, BIR is developing mobile systems that can move within a single port or border facility, relocatable systems that can be easily redeployed at different locations. ‘‘Mobility is a requirement for a few general reasons: cost, because not every port system can purchase their own system, so some ports may share a system,’‘ said Bundy. ‘‘Another reason is real estate. It’s difficult to get a commitment on one area in a port for a dedicated facility for scanning.’‘
ARACOR (Sunnyvale, CA) has experienced recent success with mobile systems, selling eight to the US Customs after a successful 1-year trial at the Port of Miami. Measurements have shown that the mobile ARACOR Eagle, which operates at 6 MeV and can penetrate more than 12’‘ of steel, provides the capability of large fixed systems. The Eagle has been in operation at the Port of Miami since early 2001.
ARACOR, L3 and BIR are only a few of the major providers of x-ray cargo inspection systems. Other players with proven track records include OSI (Hawthorne, CA), Aracor (Sunnyvale, CA), and Heimann Systems (Wiesbaden, Germany) among others. These systems typically use Varian (Las Vegas, NV) linear accelerators as the x-ray source to produce energy levels in excess of 1 MeV.
Cargo Solution = Gamma +X-ray + more?
Although x-ray systems are collecting some of the first contracts and making inroads in education and acceptance among government institutions, experts are quick to point out that isotope based systems are complimentary rather than competitive, adding that more sensors may be needed for a truly comprehensive system. In the end, they say, it’s a matter of matching the system to the application. For example, because isotope systems are significantly smaller and lighter, these systems can be integrated into truly ‘mobile’ platforms capable of driving on the highway. Local police have purchased one such system to patrol the Washington D.C. area. ‘‘You can set up a mobile system and scan parked vehicles or vehicles waiting to go through a gate, one after the other,’‘ said SAIC’s chief scientist for cargo inspection operations, Rex Richardson.
Even after all the applications for cargo inspection systems are fully defined and funding for an international cargo inspection network is identified, cargo security will continue to evolve beyond today’s technologies. HSRC’s Inbar said that countries would likely go through a second buying frenzy in a few years when next generation systems like PFNA hit the market. ‘‘Existing technologies are not designed to screen for [weapons of mass destruction] especially …bio-chem agents,’‘ Inbar said. OSI’s PFNA systems can automatically differentiate among materials based on their elemental composition. However, the system is not ready for mass production and is limited to explosives and a handful of WMD threats, Inbar said. A final solution will likely have neutron and x-ray scanning abilities, as well as bio-agent and chemical trace detection and a gamma ray detector for plutonium.
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