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Shining a light on atoms

By Kelly Foss | Oct. 30, 2012

Visualizing tiny features in a material is no small task. Atoms are much smaller than what can be seen directly, yet their arrangements often have a critical impact on how a material functions.

Memorial University professor Dr. Kris Poduska and PhD student Ben Xu recently returned from a trip to the Canadian Light Source (CLS) in Saskatoon, Sask., where they used some amazing tools for "seeing" atom arrangements.

“We have several instruments on campus that generate X-rays that allow us to look at atomic level structure, but at the CLS facility we were able to look at very particular energies of X-rays emitted by calcium atoms,” said Dr. Poduska.

She and Mr. Xu used bright beams of infrared light as well as X-rays at CLS to determine how crystallinity can affect the behaviour of calcium-containing materials in archaeological and geological settings using laboratory-synthesized comparisons.

“Calcium carbonate materials can be found in limestone, mollusk shells and archaeological plasters,” said Dr. Poduska. “What we wanted to do was to find out how the arrangement of atoms in these materials differ over three or four atom distances away from the calcium atoms. That’s a difficult thing to look at unless you have a very bright X-ray source.”

CLS is Canada’s national synchrotron research facility, and has world-class tools to study the structure and chemistry of materials at the scale of atoms. In a building the size of two football fields, CLS accelerates electrons to travel very close to the speed of light. These speedy electrons produce beams of light that are one trillion times brighter than a medical X-ray.

Dr. Poduska says calcium carbonate is present near oil reservoirs, where atomic order can affect sediment porosity, and it is the main mineral component of many marine organisms, where atomic order can provide information about past ocean climate conditions. It’s also used as a nutritional supplement, where atomic order affects how readily the body absorbs calcium.

“Obviously we can’t take every single kind of calcium carbonate sample to the synchrotron, so what we’re trying to do is develop strategies we can use that can be taken out into the field or done more conveniently on a bench top system,” she said. “The information that we’re gathering, and the ideas we’re presenting, have to be cross checked with other methods. That’s where these experiments at CLS are very unique and helpful. It’s one of the only ways we can check our understanding of the structure of these materials.

“It’s like putting together the pieces of a puzzle. We think we have a good approach laid out, but these last pieces help us really understand if our picture makes sense. What’s nice is that we will either get the answers we expected, or if we get an answer we didn’t expect, that means there’s something even more interesting going on in these materials."

Dr. Poduska says the duo collected a huge amount of data from their time at the CLS facility and they are now working on analyzing it.

“We used the X-ray source for three continuous days, took a one-day break and then were back for another four days in a row for the infrared source experiments,” she said. “When you’re trying to keep an experiment running for 72 hours you have to do a lot of planning ahead of time, and you have to be flexible because occasionally things will happen that you don’t anticipate.

“The great thing about CLS is that it’s not just a one-shot deal,” she added. “You can apply for up to two years' work, which translates into a trip to CLS approximately every six months. We have an opportunity to collect a huge amount of data, see what we might need to change in our experiments in the future and then go back to analyze different kinds of samples or to address a slightly different question.”

This was Dr. Poduska’s third visit to the CLS facility and she’s already thinking about preparing for her next visit.

“It’s very intense and exhausting, but it’s a great opportunity to do experiments we aren’t able to do here at Memorial. I highly recommend it.”