PRINCETON (US)—A lightweight, portable device could aid homeland security officials in stopping potential dirty bomb attacks. Housed in a thermos-sized container, the system issues a signal turning the laptop display bright red when nuclear material is detected.
A team from Princeton University’s Plasma Physics Laboratory (PPPL) began developing the device in 1999, not as a national security tool but rather as a way to detect exactly what “hot” elements were lacing the inner vessel of the soon-to-be decommissioned Tokamak Fusion Test Reactor. Its inner vessel had become radioactive when small amounts of tritium were injected, enabling the reactor to attain record levels of fusion power.
Ten years later, the group not only has successfully tackled that challenge, but it has won national recognition for a system that offers practical applications for homeland security and deterring radiological terrorist attacks.
The “Miniature Integrated Nuclear Detection System” (MINDS) was designed by a group led by Charles Gentile, one of the lab’s leading experts in radioactive materials.
“The development of MINDS, from a fusion energy research tool into a potentially important addition to the nation’s homeland security arsenal, illustrates an outstanding example of technology transfer from the laboratory to the marketplace,” says Lewis Meixler, PPPL’s head of technology transfer and applications research.
In December 2001, three months after the 9/11 terrorist attacks, federal authorities issued a nationwide call for devices that could detect nuclear materials that might be hidden. The idea was to guard against radiological attacks using nuclear weapons or even “dirty bombs.” Dirty bombs, also known as radiological dispersal devices, combine radioactive material with conventional explosives.
The PPPL team leapt at the opportunity to explore their device’s potential for this pressing public need.
“We knew we had something that could be of use,” Gentile says. “So we sent in the papers.”
The then-developing U.S. Department of Homeland Security received 15,000 rival proposals for funding the development of such devices. Still, the PPPL proposal stood out. The U.S. Army, through the Picatinny Arsenal in New Jersey, selected the PPPL mechanism as one of the top entries and funded it for further development.
The team had its work cut out for it. Designing the detector for indoor, in-the-lab use by a team of seasoned engineers was simple compared to what was now needed—a device that could be operated by a non-expert outdoors in an ever-changing environment. There, factors like background radiation, signals from medical radiological tests and even weather could easily skew results.
Led by Gentile, the head of tritium systems, the team also included Stephen Langish, a member of the engineering and technical staff; Andrew Carpe, a technical assistant; and software engineers Kenny Silber, Dana Mastrovito, Bill Davis, and Jason Perry.
They knew it was possible to detect radiological signals and identify their source. In the real world, the bigger problem was sorting out one from a cacophony of signals.
Levels of naturally occurring radiation from elements like radon often vary, depending on whether it rains or the temperature is high. Thousands of people each day go to medical centers where they ingest radiological dyes for imaging and treatment, emitting signals that need to be interpreted as nonhostile. Benign products, including some types of kitty litter and pottery, contain radioactive products that can be detected. And there’s the phenomenon of “scatter,” where particles bounce off objects or interfere with each other, blurring the “fingerprint” of a substance.
“You want to be able to find the needle in the haystack,” Gentile explains.
No one wanted a machine that set off an alert every time someone who has just undergone a cardiology “stress test” walked by. Nor did the designers want to miss anything significant that could be masked by such “benign” signals.
“We had to come up with a more sophisticated way to read the data,” adds Silber.
The solution, which came through years of trial and error, was found in combining two software programs using algorithms that were engineered employing techniques associated with specific characteristics of nuclear decay. The programs combined a plasma physics data strategy known as “peak fitting” and another approach employing artificial intelligence.
The look of the device has evolved with development. The three detectors are now housed in one thermos-sized container, which is attached either by wire or via wireless means to a laptop computer. Portable and easy to use, the device will issue a signal turning the laptop display bright red when nuclear material of interest is identified.
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