Cargo scanning

Intermodal shipping containers

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] In February 2009, approximately 80% of US incoming containers were scanned.^[3][4] To bring that number to 100% researchers are evaluating numerous technologies, described in the following sections.^[5]

Radiography

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^[6] 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.^[6][7] 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^[8][9] created by a linear particle accelerator (LINAC). Such X-ray systems can penetrate up to 30–40 cm of steel in vehicles moving with velocities up to 13 km/h. They provide higher penetration but also cost more to buy and operate.^[7] 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.^[10]

Dual-energy X-ray radiography

Dual-energy X-ray radiography^[11]

Backscatter X-ray radiography

Backscatter X-ray radiography

Neutron activation systems

Examples of neutron activation systems include: pulsed fast neutron analysis (PFNA), fast neutron analysis (FNA), and thermal neutron analysis (TNA). All three systems are based on neutron interactions with the inspected items and examining the resultant gamma rays to determine the elements being radiated. TNA uses thermal neutron capture to generate the gamma rays. FNA and PFNA use fast neutron scattering to generate the gamma rays. Additionally, PFNA uses a pulsed collimated neutron beam. With this, PFNA generates a three-dimensional elemental image of the inspected item.

Passive radiation detectors

Muon tomography

Cosmic radiation image identifying muon production mechanisms in Earth's atmosphere

Muon tomography is a technique that uses cosmic ray muons to generate three-dimensional images of volumes using information contained in the Coulomb scattering of the muons. Since muons are much more deeply penetrating than X-rays, muon tomography can be used to image through much thicker material than x-ray based tomography such as CT scanning. The muon flux at the Earth's surface is such that a single muon passes through a volume the size of a human hand per second.^[12]

Muon imaging was originally proposed and demonstrated by Alvarez.^[13] The method was re-discovered and improved upon by a research team at Los Alamos National Laboratory,^[14][15] muon tomography is completely passive, exploiting naturally occurring cosmic radiation. This makes the technology ideal for high throughput scanning of volume material where operators are present, such as at a marine cargo terminal. In these cases, truck drivers and customs personnel do not have to leave the vehicle or exit an exclusion zone during scanning, expediting cargo throughput.

Multi-mode passive detection systems (MMPDS), based upon muon tomography, are currently in use by Decision Sciences International Corporation at Freeport, Bahamas,^[16] and the Atomic Weapons Establishment in the United Kingdom.^[17] An MMPDS system has also been contracted by Toshiba to determine the location and the condition of the nuclear fuel in the Fukushima Daiichi Nuclear Power Plant.^[18]

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.^[19]

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.^[20] 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^[21] has led to the search for other technologies for neutron detection.

See also

• Industrial radiography
• Gamma spectroscopy

References

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 Archived 9 October 2007 at the Wayback Machine
3. Vartabedian, Ralph (15 July 2006). "U.S. to Install New Nuclear Detectors at Ports". Los Angeles Times.
4. Waste, Abuse, and Mismanagement in Department of Homeland Security Contracts (PDF). United States House of Representatives. July 2006. pp. 12–13. Archived from the original (PDF) on 30 August 2007. Retrieved 10 September 2007.
5. http://containproject.com/ CONTAIN – Container Security Advanced Information Networking
6. "Technical Specifications of Mobile VACIS Inspection System". Archived from the original on 27 September 2007. Retrieved 1 September 2007.
7. "Technical Specifications of Mobile Rapiscan GaRDS Inspection System" (PDF). Retrieved 1 September 2007.
8. "Overview of VACIS P7500 Inspection System". Archived from the original on 9 October 2007. Retrieved 1 September 2007.
9. Jones, J. L.; Haskell, K. J.; Hoggan, J. M.; Norman, D. R. (June 2002). "ARACOR Eagle-Matched Operations and Neutron Detector Performance Tests" (PDF). Idaho National Engineering and Environmental Laboratory. Retrieved 1 September 2007. {{cite journal}}: Cite journal requires |journal= (help)
10. Dan A. Strellis (4 November 2004). "Protecting our Borders while Ensuring Radiation Safety" (PDF of Powerpoint Presentation). Presentation to the Northern California Chapter of the Health Physics Society. Retrieved 1 September 2007. {{cite journal}}: Cite journal requires |journal= (help)
11. 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. Bibcode:2002PhRvS...5j4701O. doi:10.1103/PhysRevSTAB.5.104701.
12. "Muon Tomography – Deep Carbon, MuScan, Muon-Tides". Boulby Underground Science Facility. Archived from the original on 15 October 2013. Retrieved 15 September 2013.
13. "Secrets of the pyramids"
14. ""Muon radiography" by Brian Fishbine from Los Alamos National Laboratory". Archived from the original on 20 December 2013. Retrieved 18 September 2007.
15. "Muons for Peace" by Mark Wolverton in Scientific American
16. "Dr. Stanton D. Sloane of Decision Sciences looks at how passive detection systems can play their part in protecting the global supply chain" by Cargo Security International
17. "Decision Sciences Awarded Atomic Weapons Establishment (AWE) Contract for Nuclear Detection System."
18. "Cosmic Rays to pinpoint Fukushima cores" by World Nuclear News
19. "Overview of Exploranium's AT-980 Radiation Portal Monitor (RPM)". Archived from the original on 9 October 2007. Retrieved 1 September 2007.
20. "Manual for Ludlum Model 3500-1000 Radiation Detector System" (PDF). Retrieved 1 September 2007.
21. Wald, M. (22 November 2009). "Shortage Slows a Program to Detect Nuclear Bombs". The New York Times.