Applications of X-ray Fluorescence-pattern Recognition in Forensic Archaeometry and Archaeomaterials Analyses

Introduction Archaeochemists are called on to analyze a wide variety of samples, ranging from metals, pigments, and glasses to bones, stones, and soils. In most cases these samples are solids. Although non-destructive and/or micro-sample analyses are preferable for these cultural resources, in many cases there is a large amount of material available for analysis. In those instances where non-destructive analyses are critical, electron microprobe and related methods, many of which make use of X-rays, are also available. Advances have been made in X-ray fluorescence (XRF) analysis methods, such as total reflection X-ray fluorescence (TXRF) [1] that allow relatively small sample sizes (J1.L range) and detection limits well below a ppm on some samples. Although XRF methods are widely recognized for their accuracy and precision for major components, their usefulness for fingerprinting materials is less well known. Most of the literature that incorporates pattern recognition in elemental fingerprinting makes use of multi-element methods such as inductively coupled plasma (ICP) or instrumental neutron activation analysis (INAA). These other methods do offer advantages of lower detection limits for most (but not all) elements, but they are generally more destructive and expensive. For example, in ICP the sample is consumed, while in INAA it is made radioactive. Preparation of samples such as pottery for ICP analysis can also be difficult. XRF at least allows reanalysis of the same sample and in most cases the sample can still be analyzed by either ICP or INAA if that is needed. The advantage that XRF offers in its high accuracy and precision is often neglected by analysts who do not realize that it is the signal-tonoise ratio (S/N) that is most important for distinguishing samples by pattern recognition methods such as cluster analysis. A differentia-