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However, when a transparent material such as crystal or glass -- is ground into smaller pieces, its transparency disappears. As a result, a mixture of particles in a transparent glass would scatter the luminescence created by incoming gamma rays. That scattered light can't reach the photo-multiplier in a uniform manner, and the resulting readings are badly skewed.
To overcome this issue, the GTRI team reduced the particles to the nanoscale. When a nanopowder reaches particle sizes of 20 nanometers or less, scattering effects fade because the particles are now significantly smaller than the wavelength of incoming gamma rays.
"Think of it as a big ocean wave coming in," Wagner said. "That wave would definitely interact with a large boat, but something the size of a beach ball doesn't affect it."
Rare Earths and Silica
At first the team worked on dispersing radiation-sensitive crystalline nanoparticles in a plastic matrix. But they encountered problems with distributing the nanopowder uniformly enough in the matrix to achieve sufficiently accurate radiation readings.
More recently, the researchers have investigated a parallel path using glass rather than plastic as a matrix material, combining gadolinium and cerium bromide with silica and alumina.
Kahn explained that gadolinium or a similar material is essential to scintillation-type particle detection because of its role as an absorber. But in this case, when an incoming gamma ray is absorbed in gadolinium, the energy is not efficiently emitted in the form of luminescence.
Instead, the light emission role here falls to a second component cerium. The gadolinium absorbs energy from an incoming gamma ray and transfers that energy to the cer
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| Contact: John Toon jtoon@gatech.edu 404-894-6986 Georgia Institute of Technology Research News Source:Eurekalert |