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PPPL develops detection system to boost anti-terror efforts



From left are PPPL's Steve Langish, Charlie Gentile, and Andy Carpe with the miniature nuclear detection system. Photo by: El Starkman, Princeton Plasma Physics Laboratory.

Anti-terrorism efforts may get a boost from the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL). A team led by PPPL engineer Charlie Gentile is developing a miniature nuclear detection system to scan objects such as cars, luggage, and vessels for specific nuclear signatures associated with materials employed in nuclear weapons. This system could be installed at tollbooths and airports, as well as in police cruisers to detect unauthorized nuclear materials being transported.

The PPPL team of Gentile, Steve Langish, and Andy Carpe configured off-the-shelf components — a solid-state detector, multi-channel analyzer, hand-held computer, pre-amp, and amplifier — into a unique system that can determine various radiation energies, thus identifying radionuclides. It will be tuned to flag suspect signatures only; normal nuclear signatures from medical isotopes and radiography equipment would not give false positives.

This capability to differentiate radionuclides with a high degree of spatial resolution in a device that is light, small, robust, and portable makes the PPPL application unique. “We made it quite small,” said Gentile, Head of PPPL’s Tritium Systems Group.

Its robustness makes it suitable for a tollbooth or bridge entrance. A similar system using a positive intrinsic negative (PIN) diode as a detector was sent to Mars to look at radionuclides in Martian soil. “That system, like ours, is physically rugged and can take swings in environmental conditions,” said Gentile, who was involved in developing technology that used a PIN diode as a tritium detector for surface contamination in PPPL’s Tokamak Fusion Test Reactor vacuum vessel.

The PPPL-configured system includes a hand-held computer that stores databases of radionuclides for comparison, as well as three radiation detectors or heads to cover the whole gamut of nuclear signatures. The heads can include, for example, a boron trifluoride gas tube to detect neutrons; a PIN diode with a beryllium window to detect X-rays, including low-energy gamma rays; and sodium iodide crystals to detect higher energy gamma rays.

Radionuclides can be recognized and differentiated from one another since each has a distinctive energy signature or fingerprint. “Our detector looks at a fingerprint and reveals the nuclear material present,” Gentile said, adding that there are a lot of electronics that can be configured to look at a nuclear spectrum.

The unit would typically be able to detect radiation (dependent on source quantity) up to about 10 feet away and would identify the type of radiation, but not the quantity. “We can’t tell you how much source material there is, just that a particular kind of radionuclide, perhaps a transuranic or some unauthorized nuclear material, may be present. We can’t say if it’s 1,000 curies or 200 curies; our goal is to identify the radionuclide,” said Gentile.

The system could be configured with one, two, or three heads to suit the needs of law enforcement officials. For instance, airport officials might be interested in detecting materials such as cobalt or cesium that would be used in a “dirty” bomb. “Law enforcement officials would tell us what materials they might be looking for and we would tailor the configuration to detect those materials,” said Gentile.

At tollbooths or in police cruisers on the turnpike, the system would be tuned to recognize, but not sound an alarm on radioactive material from legal uses such as medical radioisotopes. “We are only interested in material found in weapons of mass destruction. The system would differentiate between approved and unapproved nuclear materials in the environment,” said Gentile.

The PPPL team is developing a library of specific spectra that would be associated with nuclear weapons. “Right now, up and down the New Jersey Turnpike, there are probably dozens of vehicles legally approved to transport nuclear materials such as medical isotopes. While a Geiger counter would detect nuclear materials in the environment, our system would detect and differentiate the materials, triggering an alarm only on those considered a risk,” said Gentile.

Added PPPL’s Steve Langish, “The system could be programmed to look only for specific nuclear fingerprints or spectra used for bomb making materials.”

It also would be able to detect some shielded materials since shielding often results in the generation of certain energy X-rays. “Our software would be tuned to look for X-ray spectra associated with specific shielding configurations,” said Gentile. He added that transuranics put out several different energies or what he termed “very interesting spectra.” A material with several specific energy peaks that the detector is scanning for may be noteworthy. “In addition, any neutron signal in the environment would be of considerable interest,” said Gentile.

Once a unit is in place, it would be up to law enforcement officials to devise an alerting system. “For instance, it could be set up at a tollbooth so that when a vehicle is flagged, a picture is taken of it and an e-mail alert goes to authorities. The vehicle would then be stopped a short distance beyond the tollbooth,” said Gentile.

The start-up cost for the whole system would be approximately $80,000, with a $17,000 price tag for each unit, not including installation charges. “This is relatively inexpensive,” Gentile said.

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