Gamma ‘camera’ eyed for security, medicine

ARGONNE, Ill. (Oct. 31, 2003) — A device originally developed for nuclear physics research may find applications in homeland security and medicine. A “Compton Camera” being developed at Argonne could be used to create detailed images of radioactive materials, from smuggled weapons to “tracers” used in nuclear medicine.

The camera uses four-inch-square sheets of germanium to detect gamma rays, a high-energy form of light produced by nuclear reactions. By using two such counters, arranged much like optical lenses, and sophisticated electronics, researchers are creating a camera that can pinpoint the origin of gamma rays to within five millimeters (about a quarter of an inch). Refined electronic analysis should improve position resolution to less than two millimeters.

If the Compton Camera meets expectations, applications for this new technology reach far beyond nuclear physics, said Kim Lister of Argonne's Physics Division (PHY). Possible uses include:

• Medical imaging: A high-resolution gamma-ray camera could offer efficient mapping of radiation in the body, enabling physicians to use lower doses of nuclear medicines. Real-time “movies” of how the nuclear medicines are absorbed may be possible.
• Homeland security: A gamma-ray camera could be used to scan shipping containers for radiation. “With this kind of position sensitivity, you’d be able to tell not just that there’s radiation somewhere inside, but the configuration of the material, and the energy of the gamma rays would tell you the type of source,” Lister said.
• Nuclear weapons verification: A gamma-ray camera could scan nuclear warheads to verify the presence or absence of fissile material. “The camera could be set to some agreed-to resolution, enough to confirm the presence of fissile material but not reveal details of the warhead’s construction,” Lister said. This would eliminate the need to actually open up the warhead, which could make such inspections more acceptable.

Future possibilities include a “zoom lens,” Lister said. The camera could be set to scan an area of possible contamination and then provide a close-up of any areas emitting gamma rays. Eventually, the device could be automated, providing emergency responders or remediation crews a “map” of contamination in a room, building or even larger areas.

Using germanium crystals to detect gamma rays has been a staple for physicists studying the atomic nucleus. At present, the world’s most sensitive gamma-ray spectrometer is Gammasphere, a $20 million, 12-ton gamma-ray “microscope” currently located at Argonne-East. It uses an array of 100 coffee-cup-sized germanium crystals to detect the faint signals from rotating atomic nuclei.

Planar Gamma-Tracking technology evolved from a series of technologies under investigation as building blocks for a next-generation instrument more powerful than Gammasphere — but only a little larger than a soccer ball, said Lister. The Gamma-Ray Energy Tracking Array, or GRETA, will be much more sensitive to gamma rays and will determine their origin with high precision.

Argonne physicists and engineers are working with their counterparts at Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory to lay the groundwork for the new device. Argonne is developing electronics and detector technologies common to GRETA and the Compton Camera.

Contributing to the Compton Camera project are Neil Hammond (PHY), Susan Fischer (PHY and DePaul University) and Filip Kondev of Argonne's Nuclear Engineering Division, who bring expertise in building devices to detect radiation. They are working in close collaboration with the detector manufacturer Ortec of Oak Ridge, Tenn. John Weizeorick of Argonne Computing and Instrumentation Solutions Division, who built much of the electronics for Gammasphere, is designing software and electronics.

“Argonne is a unique environment in which to build something like this,” Lister said. “We can combine many areas of expertise to progress very quickly.”

The researchers have working prototypes of the germanium strip detectors and hope to have the Compton Camera operational by the end of the year. After that, the camera will be “field-tested” with radioactive sources.

Frank Moore (PHY), a member Argonne’s Radiological Assistance Program team, is working with Lister to plan the field tests.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America 's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

For more information, please contact Dave Jacqué (630/252-5582 or info@anl.gov) at Argonne.