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Semiconductors could detect nuclear materials

Researchers at Northwestern University design new semiconductor material that could be part of a futuristic handheld device for spying hazardous materials, including nuclear weapons.

No one wants to stumble upon the radiation warning sign. But its presence at least indicates that hazardous materials have been detected, and that there might be some form of control of those materials.

In high-risk scenarios without up-to-date signage (war zones, abandoned testing sites, and now airport security lines), it could prove quite handy to have a handheld device that can detect hard radiation--including nuclear weapons.

Chemists at Northwestern University report in the journal Advanced Materials that they are one step closer to developing such a device.

"We have designed promising semiconductor materials that, once optimized, could be a fast, effective, and inexpensive method for detecting dangerous materials such as plutonium and uranium," says Mercouri Kanatzidis, professor of chemistry at Northwestern, in a news release.

The chemists applied a statistical method called dimensional reduction--reducing the number of variables under consideration--to the heavy element area of the periodic table (think mercury, thallium, and cesium).

In most materials, electrons are mobile enough so that gamma rays emitted by nuclear materials pass through undetected. Kanatzidis likens this to adding one drop to a bucket of water, where the change is "negligible."

By turning to dense, heavy elements, gamma rays are more easily absorbed. All the team had to do was immobilize these electrons so that when gamma rays entered the material, they would excite the otherwise obdurate electrons in an observable way, leaving a sort of signature trace.

"We needed a heavy element material without a lot of electrons," Kanatzidis said. "This doesn't exist naturally so we had to design a new material."

They were able to immobilize electrons by designing semiconductor materials to have a crystalline shape, and found that cesium-mercury-sulfide and cesium-mercury-selenide were able to detect gamma rays. Both operate at room temperature.

Kanatzidis hopes their materials could be used not only in a device to detect hard radiation, but also in biomedicine to improve diagnostic imaging.