Comparison of matrix effects on portable and stationary XRF spectrometers for cultural heritage samples

Abstract

In this work, we compare the matrix effects for two different X-ray fluorescence spectrometers, a portable and a stationary one, in order to evaluate their performances in terms of scattering radiation for different matrices. Five reference materials were analyzed: orchard leaves (NBS-1571), clay (ISE-954), bone ash (NIST-1400), 70% copper alloy (BCR-691) and 22 ct gold alloy (Fisher). The results obtained showed similar behavior for both spectrometers. The lowest background was obtained for the light matrix and an increase was observed for intermediate atomic number matrices, reaching a maximum for copper and gold alloys. In spite of that the lowest background had been obtained for the light matrix, the portable system presents a tremendously high background when compared to the stationary one. For this matrix, some of the trace elements were almost not detected by the portable spectrometer, which makes difficult their characterization with this system. For medium Z matrices there is an increase on the Compton peak and a decrease on the Rayleigh one, reaching a similar intensity. Finally, for heavy matrices, the Compton peak almost disappears and the Rayleigh effect takes the lead. Three case studies were also performed in order to appraise the behavior of the spectrometers: a paper document from the XVIII century, a sample of archaeological bone from the Middle Ages and a Portuguese coin from the XIX century.