20 July 2002
Text: Tiny Device Can Detect Hidden Nuclear Weapons
(Gallium arsenide wafer developed by Argonne National Laboratory) (660)
Researchers from the U.S. Department of Energy's Argonne National Laboratory in Illinois have developed a portable neutron detector designed to detect the hidden presence of nuclear materials.
The device, which is still undergoing testing, could help governments and international inspectors prevent smuggling and unauthorized use of nuclear weapons and materials.
The device is built around a small wafer of gallium arsenide, a semiconducting material similar to silicon. When coated with boron or lithium, gallium arsenide can detect the neutrons emitted by the fissile materials that fuel nuclear weapons.
Following is the text of a July 15 feature article issued by the Department of Energy's Office of Science:
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Feature Article Office of Science U.S. Department of Energy July 15, 2002
Tiny Device Can Detect Hidden Nuclear Weapons
Researchers from the U.S. Department of Energy's Argonne National Laboratory have developed a portable neutron detector designed to spot the clandestine presence or transport of nuclear materials.
July 15, 2002-A small, portable detector for finding concealed nuclear weapons and materials has been developed by the Argonne National Laboratory. When fully developed, the device could assist international inspectors charged with preventing smuggling and unauthorized use of nuclear weapons and materials.
The heart of the device is a small wafer of gallium arsenide (GaAs), a semiconducting material similar to silicon. When coated with boron or lithium, GaAs can detect neutrons, such as those emitted by the fissile materials that fuel nuclear weapons. Patents are pending on several detectors and their components.
The wafers are small, require less than 50 volts of power and operate at room temperature. They also can withstand relatively high radiation fields and do not degrade over time.
"The working portion of the wafer is about the diameter of a collar button, but thinner," said Raymond Klann, who leads the group from Argonne's Technology Development Division that developed the wafer and detector. "It is fairly straightforward to make full-sized detector systems the size of a deck of cards, or even smaller. Something that small can be used covertly, if necessary, by weapons inspectors to monitor nuclear facilities."
The key to detection, he said, is to coat the gallium-arsenide with something like boron or lithium. When neutrons strike the coating, they produce a cascade of charged particles that is easy to detect.
The wafers are made by inexpensive, conventional microchip-processing techniques, Klann said. They can be tailor-made for specific applications by varying the type and thickness of the coating.
Compared to other neutron detectors, Klann's detector has a number of advantages.
-- One common type of neutron detector is based on a tube of gas, which is ionized when neutrons pass through the tube. These detectors are larger in size and require more power than the GaAs detector.
-- Another common neutron detector uses silicon semiconductors. Compared to the GaAs wafer, silicon-based detectors use more power, require cooling, and degrade more quickly when exposed to radiation.
Klann's team also found that detection is improved by etching the wafer with cylindrical holes, like the dimples on a golf ball.
"We're testing various coating materials and thicknesses," he said, "as well as various combinations of hole sizes and spacings to find the best configurations for specific applications."
Klann's group has built and successfully demonstrated prototype detectors. Argonne is now looking for commercial partners interested in developing the detectors for the commercial marketplace.
Other possible uses for GaAs-based detectors include high-vacuum space applications or any other work requiring neutron detection.
-- by David Baurac
Argonne National Laboratory, the nation's first national laboratory, conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology.
David Baurac is a science writer and Director of Public Information at Argonne National Laboratory.
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