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Electronic Design

Button-Sized Wafers Sniff Out Nuclear Bombs

Researchers at Argonne National Laboratory in Argonne, Ill., have developed a small, portable detector for finding nuclear devices and materials. This technology could play a vital role in preventing rogue states and terrorist groups from building weapons of mass destruction.

The detector includes a small wafer of gallium arsenide (GaAs) coated in boron or lithium. When neutrons emitted by the fissile materials that fuel nuclear weapons strike the coating, they produce an easily detectable cascade of neutrons. The wafers can be custom-made for specific tasks by varying the coating's type and thickness.

Suitable for installation in handheld devices, these small wafers require just 50 V to operate, and they function at room temperature. They also can withstand relatively high radiation fields, and they do not degrade over time.

"The working portion of the wafer is about the diameter of a collar button, but thinner," said project leader Raymond Klann (see the figure). "It is fairly straightforward to make full-sized detector systems the size of a deck of cards, or even smaller. Something that can be used covertly, if necessary, by weapons inspectors to monitor nuclear facilities."

The wafers have several advantages over other devices. Detectors based on tubes of gas that is ionized when neutrons pass through the tube are larger and require more power than the GaAs detector. Neutron detectors that use silicon semiconductors use more power than the GaAs wafer, require cooling, and degrade more quickly when exposed to radiation.

Argonne has built and successfully demonstrated prototype detectors. The wafers are made by co-inventor Doug McGregor at Kansas State University using inexpensive, conventional microchip-processing techniques. Other applications include high-vacuum space applications and other work requiring neutron detection.

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