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Innovative glass fibers shine in radiation detection

Being flexible in the rigid world of glass radiation detectors has made Pacific Northwest National Laboratory's glass fiber optic detectors very popular.

The lightweight glass optical fibers, developed at PNNL in the '90s, emit a light at the end of the fiber when hit by a neutron or gamma ray, the first glass fiber to react to radiation energy. The light is enhanced by a photomultiplier tube at the end of the fibers, which allows the light to be visible without special light sources. The fibers are being commercialized by NucSafe of Tennessee to be imbedded in roads at border crossings to detect nuclear materials smuggling. These fibers are the first viable way to monitor large areas for radionuclides, such as plutonium, since previous detectors were solid helium-filled gas tubes, which could not be imbedded in roads or used to monitor large areas.

NucSafe scientist Rick Seymour said that they are working hard to keep up with the demand for the popular glass fibers. "Our clients include the Department of Homeland Security, the Department of Defense, the U.S. Coast Guard, the U.S. Navy, Customs and Border Protection, and we also have systems in the United Kingdom, Denmark, Estonia, Poland, Lithuania, Germany, Austria and Russia," Seymour said.

PNNL scientists were originally discouraged by other materials engineers from researching glass fiber technology for radiation detection, since many said it was impossible. But by working with the glass chemistry over several years, scientists were able to create a high-quality glass with lithium and cerium that was transparent enough to detect radionuclides.

PNNL also built a fiber draw tower from the ground up, which is used to turn the melted glass into the flexible fishing line-like fiber. The tower was unique to the Laboratory since previously available draw towers would not have allowed them to make fibers that detected radiation. Most optical fiber draw towers pulled fibers like taffy. "We had to use a hot down-draw process," said Mary Bliss, a chief scientist at PNNL. "Our glass is so high in cerium and lithium that it would just grow crystals if we tried to pull it like taffy," which would ruin the fiber.

The hot down-draw process refers to the way the tower pulls the melted glass down through a platinum bushing and coats the resulting fiber with silicone before sending it further down into an insulated container that cools the fiber.

The draw tower was so well-constructed for neutron and gamma detecting glass fibers that PNNL assisted NucSafe in building an updated version after it licensed the technology.



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