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Spectroscopies Offer Integrated View

Photonics Spectra
Jun 1999
Barbara Grant

Two scientists who integrated data from four spectroscopy methods have found an innovative way to test hazardous materials and aging nuclear weapons stockpiles. The technology will provide images of heterogeneous materials that will allow scientists to gain a better understanding of their chemical composition.

Developed by Jon Schoonover and George Havrilla, research chemists at the US Department of Energy's Los Alamos National Laboratory, the technique is known as Mesoscale Chemical Imaging. It combines the elemental analysis technologies of micro-x-ray fluorescence spectroscopy and scanning electron microscopy with the molecular analysis technologies of Raman and infrared spectroscopies "to give a more comprehensive chemical characterization" of a sample than either analysis alone can provide, Havrilla said.

He noted that, although micro- x-ray fluorescence can identify the element calcium in a quartz sample, it cannot provide information on its mineral phase. Infrared and Raman spectroscopies can identify carbonate bands but cannot confirm the presence of calcium. The new technique's unique feature lies in integrating the methodologies to determine the sample's chemical characterization precisely.

George Havrilla looks through a Raman imaging microscope used as part of the Mesoscale Chemical Imaging process developed with Jon Schoonover, right. Courtesy of Los Alamos National Laboratory.

Each instrument uses its own imaging platform. For example, the researchers are using a Falcon Raman imaging microscope system provided by ChemIcon Inc. of Pittsburgh and an IRplan microscope from Spectra-Tech Research in Shelton, Conn., combined with a 20SXB Fourier transform infrared spectrometer from Nicolet Instrument Corp. of Madison, Wis. Image registration, instrument spatial resolution and field of view are some of the many issues that they must address to successfully combine the data.

The lab is also developing hardware that combines micro-x-ray fluorescence and micro-Raman imaging technologies. Schoonover expects the system to provide data by the end of this year.

Nondestructive sampling

Nondestructive characterization of small amounts of actinides such as uranium, neptunium and plutonium increases safety margins, Schoonover noted. He added that diagnosing a change before it becomes a problem is critical to successful monitoring of aging weapon components.

"The integrated approach can demonstrate a distribution of elements or a molecular-level change which is not readily apparent," he said. It could also find applications in several other areas in materials science, chemistry and biology.

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