Empirical study of the effect of count time on the precision and accuracy of pXRF data

As a cost-effective and non-destructive method for multi-element analysis, portable X-ray fluorescence spectrometry (pXRF) has the potential for broad archeological application; however, recent applications of pXRF remain inconsistent. For example, sourcing studies using pXRF have irradiated artifacts and geologic source materials for widely varying amounts of time. In this study, we investigate the effect of count time on the precision and accuracy of pXRF data obtained for two geologic standards, as well as for obsidian, fine-grained volcanic (e.g., andesites, dacites), metamorphic, and chert specimens from the North American Great Basin. We find that the precision and reliability of pXRF data does not improve significantly at count times greater than 180 s. Our analysis also indicates that count time has little bearing on the accuracy or validity of pXRF data, as expected from the mathematical relationships between count time, intensity, and concentration. Finally, we demonstrate that a well-calibrated pXRF instrument generates compositional data comparable to data obtained using other analytical methods. We offer this study as a step toward the development of a consistent and rigorous analytical protocol for archeological applications of pXRF.