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TSA Disputes Research on Airport Scanners

Two former physics professors say the controversial X-ray scanners will not detect explosive material that is flat and attached to a person’s abdomen.

A TSA approved advanced imaging scanner in use. Photo courtesy of the Transportation Security Administration
The U.S. government disputes research by two former physics professors who say the controversial X-ray scanners used for security screenings at airports will not detect explosive material that is flat and attached to a person’s abdomen.

In response to a request by Government Video, the Transportation Security Administration (TSA) provided a written statement that indirectly denies the findings of Joseph Carlson and Leon Kaufman, both former physics professors at the University of California-San Francisco who studied the effectiveness of airport X-ray “backscatter units.”

The professors issued a report—An Evaluation of Airport X-ray Backscatter Units Based on Image Characteristics—that was published by The Journal of Transportation Security published as a peer-reviewed article. The report says, “that although images can be made at the exposure levels claimed, detection of contraband can be foiled in these systems.”


According to the report, the reasons contraband might not be detected are because of the X-ray exposure level produced by the scanner combined with how a substance such as plastic explosives are placed on a persons body. Those factors can prevent the material from being detected by the scanner, the study says. In addition, “because front and back views are obtained (in a scan), low Z (metal) materials can only be reliably detected if they are packed outside the sides of the body, or with hard edges, while high Z materials are well seen when placed in front or back of the body, but not the sides.”

“Even if exposure were to be increased significantly, normal anatomy would make a dangerous amount of plastic explosives with tapered edges difficult, if not impossible, to detect,” the study says.

Furthermore, objects as large as 15 to 20 centimeters in diameter that are “irregularly-shaped,” and about a centimeter thick, taped to the abdomen, “would be invisible to this (scanner) technology,” because such an object “is easily confused with normal anatomy.” Thus, “a third of a kilo” of plastic explosives shaped like a pancake “would be missed by backscatter high technology,” the report says.

T he research reveals there is an assumption that the X-ray machine will be performing at 100 percent efficiency, an assumption the professors’ dispute. The performance of the X-ray machines is “heavily influenced by the number of units and budget, and little influenced by competitiveness and performance,” therefore, “the efficiency (of the scanners) may easily be 50 percent.”

Nonetheless, the TSA says, “Advanced imaging technology is a proven, highly-effective tool that safely detects both metallic and non-metallic items concealed on the body that could be used to threaten the security of airplanes.”

“TSA employs many layers of security that work collaboratively to form a system that gives us the best chance to detect and disrupt the evolving threats we face,” the agency’s statement says.