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Archaeologists revolutionize field research using pXRF with GIS

Sharp and Litschi with pXRFArchaeologists Kayeleigh Sharp (pictured, left) and Melissa Litschi (pictured, right) are combining two established technologies in highly innovative and productive ways to revolutionize their field research.

The university has acquired a portable X-ray fluorescent analyzer or pXRF, as it is known, which looks like a ray-gun from a Star Trek episode but which has the capacity to analyze—to qualify and quantify—any given material for virtually any element from magnesium to uranium.  

The portability of the handheld model allows archaeologists like Sharp and Litschi to make determinations about chemical composition on site, without having to destroy specimens, haul materials, or export samples back to the lab for analysis. Since they do field work principally in South America, the savings of time and expense are considerable. This versatility of the pXRF means that large, fragile or otherwise immovable objects—fragile rock art, for example—can be analyzed quickly for the very first time.

When Litschi and Sharp combine the results of XRF spectrometry with GIS the results have been nothing short of spectacular, yielding lush, detailed maps of what was found where over a large area of an archaeological site on the north coast of Peru, in Sharp’s case, and soon to be in the Peruvian highlands for the first time, in Litschi’s case.  

Arrival on campus

Professor Izumi Shimada, who advises Sharp and Litschi and has sought to bring the portable device to SIU, credits Interim Vice Chancellor of Research James (Jim) Garvey with immediately recognizing the benefits a pXRF would bring to research across campus. Garvey tipped-in general research funds to enable principal contributor Department of Geology, along with lesser contributors Department of Anthropology and Center for Archaeological Investigations (CAI), to meet the asking price of $48K for the unit.

The pXRF arrived on campus in June 2014, and has been in heavy demand ever since. Its use is governed by amount of contribution but the schedule is amicably maintained by Professor Sue Rimmer of Geology.

According to Shimada, the technology itself has existed for many decades. What is new is that the equipment is now portable. Akin to the laptop, the device can now be taken outdoors, “to wherever the artifacts may be.” Says Shimada, the pXRF is “versatile, non-destructive, portable and precise.”

The uses to which the pXRF may be put depend only on creativity—virtually anything which calls for chemical composition analysis can either be placed under the little leaded “top hat,” or aimed at by the laser gun-type device. Widely used in industry for quality monitoring, it is also an invaluable tool for scholarly research. For example, the Center for Archaeological Investigations made the first use of SIU’s pXRF to analyze a rare mastodon bone recently donated to the CAI. It was the first such bone found in Jackson County, and the device was used to try to discover what had caused the pronounced staining which appears on the surface. The analysis carried out by Sharp and Litschi confirmed that the stains were manganese, meaning that they can be attributed to the watery environment in which the bone had been deposited for thousands of years.  According to Sharp and Litschi, “the great advantage of using the pXRF was that our simple question could be answered in real-time, freeing us to pursue other lines of inquiry.”

As the unit is put to more and more use, Shimada very much hopes that the university will acquire more of them. Intensely used by faculty and graduate students in various fields, he fears that there soon will be problems with graduate researchers such as Sharp and Litschi gaining access for their prolonged summer field research. 

How it works

Litschi and Sharp use pXRF machineWhen any given material is bombarded by X-ray, the reaction is an emission in the form of light—fluorescence. Energy level and intensity of this this light/fluorescence is measured by a sensitive, built-in detector which identifies any chemical elements present and their respective concentrations. The specially-designed software on a connected laptop captures the information in readily understandable graphic and numerical form which develops almost immediately onscreen. Says Sharp, “It’s remarkable to be able to look at the preliminary results of your analysis as it takes place before your eyes.”

Analysis may be performed in one of two ways. Either a small piece of material may be placed on the aperture from which X-Ray is emitted (under the protective safety lid) or the researcher can simply “point and shoot.” Shimada notes that the sought-after information is obtained rather quickly, in as little as 15 seconds, though Sharp explains that more time is needed to increase accuracy on scientific samples. Generally, the most reliable readings are taken for over a minute, and sometimes as long as three minutes. By any definition, this is fast.    

No waiting

One of the things Kayeleigh Sharp has been able to do in her research with the pXRF is to examine two different types of pottery fragments coexisting at the same site on the north coast of Peru, to determine whether they are made of the same materials or not and by the same populations or not. She is detailing other lines of data with data from the pXRF, using GIS to statistically map patterns of distribution to determine which types of pottery were in use where. She hopes to determine whether these were two segments of the same population or two completely different populations living side-by-side.  (Clustering in different structures may indicate two different groups.) Using the pXRF in conjunction with GIS allows her to test data in spatial context.

Meanwhile, in the Peruvian highlands, Melissa Litschi plans to utilize the device to test composition of soils to determine what kinds of activities may have taken place at different locations, which is where her use of GIS comes in. Her focus, then, is on examination of the trace elements blooming up onscreen during an assay, and what that may tell us about past activities and their organization. Litschi notes that “different human activities, [such as food consumption and craft production], leave a distinctive chemical signature on the earth which is detectable using pXRF.”

Working in this new way with these combined technologies has been extremely exciting for both scholars. As archaeologists, prior to working with the pXRF neither Smart nor Litschi had much chemistry under her belt. The technology has driven both to expand their knowledge base in chemistry, enabling them to ask increasingly more nuanced questions of the artifacts.

The equipment has forged cross-campus cooperation among disciplines, as well. Sharp says she hopes that familiarity with the technology will be an asset when she looks for an academic post, but “what’s really nice is that we’re working with geology and a broader range of scholars from other disciplines and other academic departments here at SIU.”

L. A. Brown

Shimada, Smart and Litschi demonstrated the pXRF and contributed technical information for this spotlight.