Nanophotonic Detector Targets Nuclear Terrorism

A new technique for detecting radiation will increase the effectiveness of nuclear surveillance, allowing security officials to easily find and prevent the smuggling of radioactive materials.

The two most common radiation detectors used today fall under two categories: scintillation detectors and solid-state detectors. Both kinds of detection have drawbacks, however.

Scintillators normally are made out of a single crystal that creates light flashes when a gamma ray strikes it; these crystals are difficult to produce, and tend to be fragile and cumbersome. Solid-state detectors are based on semiconducting materials and register such rays as electrical pulses. However, the semiconducting materials necessary to make these detectors must be kept at extremely low temperatures, making them difficult to apply in the field.

Researchers at the Georgia Tech Research Institute worked around these issues by developing the Nano-photonic Composite Scintillation Detector, a prototype that combines rare-earth elements and other nanoscale materials to increase the effectiveness of scintillation-style detectors.

Georgia Tech Research Institute researchers Brent Wagner (l) and Bernd Kahn are using novel materials and nanotechnology techniques to develop improved radiation detection. (Credit: Gary Meek)

“US security personnel have to be on guard against two types of nuclear attack — true nuclear bombs, and devices that seek to harm people by dispersing radioactive material,” said Bernd Kahn, the principal investigator on the project. “Both of these threats can be successfully detected by the right technology.”

He and co-principal investigator Brent Wagner led the team that developed a novel scintillation material using gadolinium and cerium bromide combined with silica and alumina, which they suspended in a glass matrix. Gadolinium is essential to scintillator detectors because it is an absorber. However, in this system, the gamma ray energy absorbed by gadolinium is not sufficiently converted into visible light. Instead, the gadolinium absorbs the energy and transmits it to the cerium bromide, which releases the energy in the visible spectrum.

The researchers found that by melting the four components together and letting them cool into a block, they could distribute the gadolinium and cerium throughout silica-based glass types.

Examples of scintillators that the researchers produced from molten glass. The wormlike blue structure is an artifact from the glass-molding process. (Credit: Gary Meek)

“A nanopowder can be much easier to make, because you don’t have to worry about producing a single large crystal that has zero imperfections. We're optimistic that we've identified a productive methodology for creating a material that could be effective in the field,” Wagner said. “We’re continuing to work on issues involving purity, uniformity and scaling, with the aim of producing a material that can be successfully tested and deployed.”

The research aims to support US security forces in safeguarding the country against nuclear terrorism. These nanoscintillators will be able to detect dangerous radiation from nuclear materials that may be smuggled through airports, or across border crossings.

The research was supported by the Domestic Nuclear Defense Office of the Department of Homeland Security and the National Science Foundation.

The results were presented at the SPIE Defense, Security, and Sensing Conference in Baltimore on April 23.

For more information, visit: www.gtri.gatech.edu