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New Mexico State University

New Mexico State University

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New research tool being utilized at NMSU

Researchers from New Mexico State University are replacing magnifying glasses, fingernails and diluted hydrochloric acid - the rock identification tools of field geologists - with Laser-Induced Breakdown Spectroscopy (LIBS), a technique that holds great potential for the science of geology and much more.

Geology majors Austin Hanson (left) and Carlos Montoya demonstrate a newly developed geochemistry technique known as laser-induced spectroscopy breakdown. Hanson and Montoya, along with their faculty adviser, Nancy McMillan, will give a presentation on their research at the Geological Society of America (GSA) conference later this year. (NMSU photo by Darren Phillips)

The LIBS laser focuses a pulse of light on the material, causing atoms to lift off the surface and ignite into a plasma at a temperature of 15,000K (compared to the Sun's meager 6,000K). As the plasma cools, electrons relax back into their low-energy levels and emit photons of light. An optic fiber cable catches the light produced and feeds the information into a spectrometer that delivers the results in a combination of wavelength versus intensity on a computer.

There is virtually no preparation and results are instantaneous. The benefits of using LIBS to identify materials have been well known, but now it is portable and requires only an electric generator to operate in the field. It is hoped that by 2009 a backpack model will be available, according to science journals.

Though its creation was an evolving and gradual process, most of the credit for LIBS goes to a team at Los Alamos Laboratory in the 1980s. However, limitations in the capability of computers prevented many applications from being possible. Now that computer technology has caught up with LIBS, the possibilities appear endless.

Nancy McMillan, department head and professor of geology at NMSU, is most interested in its geological applications. Processes for identifying minerals and other substances in the field described as "cut and polish" or "grind and fuse" have now been substituted with the simple instruction of "point and click."

LIBS takes the guess work out of identifying substances. Sight identification and hardness tests are able to narrow down the possibilities greatly, but chemical variations that can determine the kind of stone are undetectable by those means.

The method also allows for conclusive testing to be done on tiny amounts of material, thereby limiting the damage to precious stones and archaeological materials such as paint.

McMillan said that the current method does leave a mark on the substance tested, a tiny crater with a width of about 400 microns (compared to a human hair at 30-60 microns). This disfigurement is particularly frustrating for those dealing in gems. McMillan has received a grant from the state of New Mexico to work with Raydiance, Inc. and their ultrashort pulse lasers to find less damaging techniques for specific gems.

Seven NMSU undergraduate geology students will give presentations on their findings from LIBS laser research at the Geological Society of America national conference this October in Houston, she said.

One project addresses using LIBS to determine the origin of particular gemstones, since the provenance of a gemstone greatly affects its worth. Another project deals with the ability of LIBS to analyze lithium content, which is so lightweight that it is traditionally very difficult to measure. A third research project uses LIBS to measure the amount of sulfur and heavy metals in crude oil. The results can indicate when the drilling has reached another level, something that currently takes weeks to accomplish. Other projects focus on correlating the chemical make up of rocks from different places and the workings of the LIBS instrument itself.

"We are giving our students a forefront into this new area," McMillan said. "As an Aggie I'm excited to be able to hand my students that kind of opportunity."

She said that while many universities are currently using LIBS, only a few geology departments are using it to study Earth materials.

"Our students get the opportunity to experience fundamental research and think about processes and applications that have little precedent," McMillan said. "There is a lot of trial and error because no one has gone before to develop a template or set of procedures. So, the students have a greater understanding of the scientific method and the way science progresses."

The future applications of LIBS are vast and far-reaching. "Standoff" LIBS uses a telescope to replace the fiber optic cable, allowing the device to take measurements of objects from several meters away. This type of measurement would be extremely useful in toxic environments, for identifying land mines, to retrieve fingerprints from unsafe areas and in space. Currently standoff LIBS are retrieving data from up to 50 meters away and it may be possible to use them from a distance of 100 meters.

"The students are positioning themselves for exciting jobs as this technology hits geoscience industries and they are the people in their generation that are already trained," McMillan said.