Characterisation of Ancient Coins Made in Silver-Copper Alloy by Means of Micro-PIXE

A study to analytically characterise ancient coins has been started by the Solid State Physics group of the Torino University and INFN in 2010. This topic is particularly interesting for numismatic and archaeometry, because it allows to evaluate commercial exchanges among tribes, to hypothesize relative chronologies, to verify the presence of a debasement along the years and to investigate the exchange ratios among different emissions of coins. Until now the study has been focused on coins made of a silver-copper alloy in the Roman and pre-Roman period. The samples made of this material are often characterised by surface silver-enriched layer and, for this reason, some silver coins have been cut to study their microstructure and especially to assess the absence or the presence (and in this case also the size), of corrosion layers, enriched layers and inhomogeneity between surface and bulk. Some papers in literature have already discussed the topic and some preliminary measurements on one coin have already been performed at LNL in last years.