Tiny Device Can Detect Hidden Nuclear Weapons, Materials

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 Argonne 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 have 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