Neutrons seek bombs

The federal government has deployed an advanced detection system at a commercial cargo screening facility in southwestern Texas that cannot only identify the type of explosives, chemical agents, radioactive devices, and narcotics, but the precise location of such materials within a truck.

It's the first field operational deployment of the pulsed fast neutron analysis (PFNA) system, which cost about $10 million. It can penetrate densely packed cargo and doesn’t require human screeners to interpret images.

Peter Kant, vice president of government affairs for Rapiscan Systems, which developed the system, said the PFNA system combined with other detection systems at the cargo screening facility in Ysleta, which is located near El Paso, Texas, provides screeners with a higher confidence in machine inspections and almost eliminates the need for manual inspections.

With the PFNA system, a truck is pulled through what "looks like a big carwash," he said. A beam of neutrons is shot into the truck and the system divides the truck’s cargo into voxels, which are the smallest distinguishable box-shaped part of a three-dimensional image. The system detects the elemental composition of each voxel, such as the content of hydrogen, nitrogen, helium, oxygen and others, he said.

"What PFNA does is it inspects the container using neutrons and it can count up the individual atoms in that container," Kant said. PFNA technology was developed in the late 1980s and early 1990s through Defense Advanced Research Projects Agency funding.

The amounts of these elements, or their elemental signature, can be used to distinguish one type of material from another. The system is pre-programmed or pre-loaded with the elemental signatures of all explosives, chemical agents, nerve gases, radioactive materials, contraband, and narcotics, he said. When the system scans the truck, it creates something that looks like an image indicating where the potential explosive or chemical agent is located within the truck, Kant added.

"What that means is instead of someone interpreting an image it’s telling you exactly what is there," he said. "And you can preload it for almost anything you can find: U.S. currency, sugar, rice, olive oil, contraband materials, durable goods, stainless and carbonized steel."

The machine can be tweaked to detect smaller quantities of explosives or its database expanded to include elemental signatures of other nerve agents, for example. The false alarm rate, Kant said, is below one percent.

The Customs and Border Protection agency will test the PFNA technology for 120 days at the Ysleta site -- which is one of the busiest border crossings in the country -- but it will also see how the PFNA system works in the layered screening approach with the gamma radiographic and high-energy X-ray detection systems that are also used there.

Gamma systems, which are the most commonly used detection machines used at border crossings and cost about $1 to 1.5 million, have the least penetration of all detection systems and produce the lowest image resolution, Kant said. But he added they can see into about 40 percent of the inspected cargo.

The high-energy X-ray technology, which was developed by Rapiscan and was deployed at the Ysleta screening facility last year, has the ability to penetrate about 95 percent of the remaining uninspected cargo. Each of those systems cost about $4 to $5 million. Screeners must interpret the images created by these two systems. Kant said that usually if they are unsure about what they see, they will then manually inspect the cargo.

However, the PFNA technology is able to penetrate the remaining cargo and provide screeners with a better handle on what is there, he said. The combined approach of using such machines almost eliminates the need for manual inspection of cargo and could speed commerce. He said it takes about 15 man hours to unload a truck in order to inspect it.

"It isn't inspection that slows down throughput and commerce, it's the wrong inspection," he said.

The Transportation Security Administration will deploy similar Rapiscan-developed PFNA systems at Houston’s George Bush Intercontinental Airport and the Ted Stevens Anchorage International Airport in Alaska, which is the busiest air cargo airport in the nation, Kant said.


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