Cargo scanning

Cargo scanning or non-intrusive inspection (NII) refers to non-destructive methods of inspecting and identifying goods in transportation systems. It is often used for scanning of intermodal freight shipping containers. In the US it is spearheaded by the Department of Homeland Security and its Container Security Initiative (CSI) trying to achieve one hundred percent cargo scanning by 2012[1] as required by the US Congress and recommended by the 9/11 Commission. In the US the main purpose of scanning is to detect special nuclear materials (SNMs), with the added bonus of detecting other types of suspicious cargo. In other countries the emphasis is on manifest verification, tariff collection and the identification of contraband.[2] At February 2009, approximately 80% of US incoming containers are scanned.[3][4] In order to bring that number to 100% researchers are evaluating numerous technologies, described in the following sections.



Gamma-ray radiography

Gamma-ray image of a shipping container showing two stowaways hidden inside
Gamma-ray image of a truck showing goods inside a shipping container
A truck entering a gamma-ray radiography system

Gamma-ray radiography systems capable of scanning trucks usually use cobalt-60 or caesium-137[5] as a radioactive source and a vertical tower of gamma detectors. This gamma camera is able to produce one column of an image. The horizontal dimension of the image is produced by moving either the truck or the scanning hardware. The cobalt-60 units use gamma photons with a mean energy 1.25 MeV, which can penetrate up to 15–18 cm of steel.[5][6] The systems provide good quality images which can be used for identifying cargo and comparing it with the manifest, in an attempt to detect anomalies. It can also identify high-density regions too thick to penetrate, which would be the most likely to hide nuclear threats.

X-ray radiography

X-ray radiography is similar to Gamma-ray radiography but instead of using a radioactive source, it uses a high-energy Bremsstrahlung spectrum with energy in the 5-10 MeV range[7][8] created by a linear particle accelerator (LINAC). Such X-ray systems can penetrate up to 30–40 cm of steel[9][10] in vehicles moving with velocities up to 13 km/h. They provide higher penetration but also cost more to buy and operate.[6] They are more suitable for the detection of special nuclear materials than gamma-ray systems. They also deliver about 1000 times higher dose of radiation to potential stowaways.[11]

Dual-energy X-ray radiography

Dual-energy X-ray radiography[12]

Backscatter X-ray radiography

Backscatter X-ray radiography

Muon radiography

Muon radiography.[13][14][15]

Neutron activation systems

Examples of neutron activation systems include: Pulsed Fast Neutron Analysis (PFNA) and Thermal Neutron Activation (TNA) – which detect gamma-rays created when neutrons interact with matter.

Passive radiation detectors

Truck going through Radiation Portal Monitor

Gamma radiation detectors

Radiological materials emit gamma photons, which gamma radiation detectors, also called Radiation Portal Monitors (RPM), are good at detecting. Systems currently used in US ports (and steel mills) use several (usually 4) large PVT panels as scintillators and can be used on vehicles moving up to 16 km/h.[16]

They provide very little information on energy of detected photons, and as a result, they were criticized for their inability to distinguish gammas originating from nuclear sources from gammas originating from a large variety of benign cargo types that naturally emit radioactivity, including bananas, cat litter, granite, porcelain, stoneware, etc.[4] Those Naturally Occurring Radioactive Materials, called NORMs account for 99% of nuisance alarms.[17] Some radiation, like in the case of large loads of bananas is due to potassium and its rarely occurring (0.0117%) radioactive isotope potassium-40, other is due to radium or uranium that occur naturally in earth and rock, and cargo types made out of them, like cat litter or porcelain.

Radiation originating from earth is also a major contributor to background radiation.

Another limitation of gamma radiation detectors is that gamma photons can be easily suppressed by high-density shields made from lead or steel,[4] preventing detection of nuclear sources. Those types of shields do not stop fission neutrons produced by plutonium sources, however. As a result radiation detectors usually combine gamma and neutron detectors, making shielding only effective for certain uranium sources.

Neutron radiation detectors

Fissile materials emit neutrons. Some nuclear materials, such as the weapons usable Plutonium-239, emit large quantities of neutrons, making neutron detection a useful tool to search for such contraband. Radiation Portal Monitors often use Helium-3 based detectors to search for neutron signatures. However, a global supply shortage of He-3 [18] has led to the search for other technologies for neutron detection.

Gamma spectroscopy

See also


  1. ^ "100% Cargo Scanning Passes Congress" article in "FedEx Trade Networks" (Aug. 02, 72007)
  2. ^ U.S. Azerbaijan Chamber of Commerce - SAIC'S VACIS(R) Cargo, Vehicle and Contraband Inspection Systems to Be Installed in Azerbaijan
  3. ^ Vartabedian, Ralph (July 15, 2006). "U.S. to Install New Nuclear Detectors at Ports". The Los Angeles Times. 
  4. ^ a b c Waste, Abuse, and Mismanagement in Department of Homeland Security Contracts. United States House of Representatives. July 2006. pp. 12–13. 
  5. ^ a b "Technical Specifications of Mobile VACIS Inspection System". Retrieved Sep. 2007. 
  6. ^ a b "Technical Specifications of Mobile Rapiscan GaRDS Inspection System". Retrieved Sep. 2007. 
  7. ^ "Overview of VACIS P7500 Inspection System". Retrieved Sep. 2007. 
  8. ^ 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. Retrieved Sep. 2007. 
  9. ^ "Technical Specifications of VACIS P7500 Inspection System". Retrieved Sep. 2007. 
  10. ^ "Technical Specifications of Rapiscan Eagle Inspection System". Retrieved Sep. 2007. 
  11. ^ Dan A. Strellis (2004-11-04) (PDF of Powerpoint Presentation). Protecting our Borders while Ensuring Radiation Safety. Presentation to the Northern California Chapter of the Health Physics Society. Retrieved Sep. 2007. 
  12. ^ Ogorodnikov, S.; Petrunin, V. (2002). "Processing of interlaced images in 4-10 MeV dual energy customs system for material recognition". Physical Review Special Topics: Accelerators and Beams 5 (10): 104701. doi:10.1103/PhysRevSTAB.5.104701. 
  13. ^ "Muon radiography" by Brian Fishbine from Los Alamos National Laboratory
  14. ^ "MU-Detector - a Novel Method of Detecting Nuclear Weapons, Dirty Bombs and Voids in Cargo"
  15. ^ "Muons for Peace" by Mark Wolverton in Scientific American
  16. ^ "Overview of Exploranium's AT-980 Radiation Portal Monitor (RPM)". Retrieved Sep. 2007. 
  17. ^ "Manual for Ludlum Model 3500-1000 Radiation Detector System". Retrieved Sep. 2007. 
  18. ^ Wald, M. (November 22, 2009). "Shortage Slows a Program to Detect Nuclear Bombs". New York Times. 

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