pXRF: a study of inter-instrument performance

Integrating portable X-ray fluorescence (pXRF) instrumentation into archaeological investigations has generated as much interest as skepticism because several characteristics of the technique limit analytical accuracy and precision. This paper seeks to explore inter-instrument performance in order to assess the potential pXRF instrumentation has in examining the elemental composition of lithic raw materials. Two pXRF instruments, Delta and Omega models both manufactured by Olympus Innov-X Systems, were utilized to obtain the trace element signatures of five fine-grained volcanic sources and four obsidian sources in the Great Basin. We compared the two portable instruments to a wavelength-dispersive instrument extensively calibrated with geologic standards and to a commercial benchtop energy-dispersive system. Our results suggest that the relationships between the data produced by these different instruments are complex, and as we look to the future of pXRF use in archaeological analysis we argue that that the same strict protocols applied in laboratory-based XRF analyses, involving instrument calibration, evaluation of inter-instrument performance, and comparison to accepted geologic standards, need to be applied in pXRF analysis.     

Parameters in the use of pXRF for archaeological site prospection: a case study at the Reaume Fort Site,Central Minnesota

Field portable/hand-held x-ray fluorescence (pXRF) analyzers have been characterized as potentially useful for archaeological site prospection, but little has been published on the parameters of their use in this manner. The purpose of this study is to explore whether the variability of surface geochemistry as characterized with a pXRF analyzer corresponds with subsurface archaeological features at a site subsequently excavated, and what conditions influence the success of this endeavor, including feature depths, soil moisture, and sample processing. A 520 m² within-site area was systematically surveyed on a 2 m interval, within which several types of archaeological features were excavated (chimney bases, wall trenches, and a bonebed of faunal waste), taking readings in situ and collecting samples for ex situ testing (undried, dried but not powdered, and dried/powdered). The four different tests of each grid location, analyzed through univariate and multivariate tests, showed that the pXRF surface data does correspond with some types of subsurface features when those features are very shallow (within 5 cm of surface level) and are associated with clayey fills. Further, the data from the subsurface samples provides excellent distinction of feature fills from other sediments, regardless of sample preparation. In situ surface survey with pXRF analyzers may however be adequate for sites with a thorough baseline geochemical database.     

Trade,tribute, and neutron activation: The colonial political economy of Xaltocan,Mexico

In Trade, Tribute, and Transportation, Ross Hassig argues that indigenous towns in the northern Basin of Mexico during the colonial period were largely self-sufficient. They traded with Mexico City mostly in elite goods, but for the most part they produced for their own subsistence or traded with nearby towns. Chemical characterization by instrumental neutron activation analysis (INAA) and portable X-ray fluorescence (pXRF) of ceramics and obsidian from post-conquest contexts in Xaltocan, a site in the northern Basin of Mexico, reveals that Hassig’s model is partly correct for describing Xaltocan. The town focused on trade with nearby towns and it produced some ceramics for local consumption. However, Xaltocan was hardly isolated and self-sufficient in the post-conquest period. Instead, the data suggest that the people of Xaltocan also obtained ceramics and obsidian from a greater variety of sources than under Aztec domination. Rather than being an isolated rural site, Xaltocan either increased its external connections and number of trading partners after the Spanish conquest, or it managed to obtain a greater variety of products than before through a bustling market system.