A fast-integrated x-ray emission spectrometer dedicated to the investigation of Pt presence in gold Celtic coins (3rd-1st century BCE)

With this study, we present the development of a transportable x-ray emission spectrometer (XES) that was realized in a net time of 20 h, in order to verify the presence of Platinum (Pt) in gold Celtic coins belonging to 3rd-1st century BCE. Prior to the XES study, measurements using Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) revealed that the coins were made of highly concentrated gold (Au) alloy with trace amounts of bismuth (Bi) and, in one case, osmium (Os) and iridium (Ir). Os and Ir together with Pt and other components belong to the Platinum Group Elements (PGE). They form inclusions in ancient gold alloys and their presence is significant in provenance studies since they indicate the use of alluvial gold. Detection of platinum trace elements in a golden matrix is not possible using energy dispersive x-ray emission techniques (SEM-EDS, ED-XRF, or PIXE) because of the limited energy resolution of the Si detectors. A way to overcome this problem is by using a high-resolution wavelength dispersive x-ray emission technique. For this purpose, we built a crystal spectrometer in Von-Hamos geometry. In the framework of this study three samples/coins have been measured, and the presence of Pt was verified in one of them. The limitations of our spectrometer are critically evaluated and ways to optimize the performance of the spectrometer are discussed.