Compositional and microstructural characterization of Celtic silver coins from northern Italy using neutron diffraction analysis

The silver coinage of Celtic tribes settled in northern Italy (IV–I century B.C.) is a topic characterized by several issues, such as chronology, attributions and relationships between emissions produced in different periods. In order to provide numismatists with new data, several specimens, belonging to different typologies, have been analysed with neutron diffraction technique to overcome surface alteration and to provide bulky compositional and structural information of the coins. Measurements performed with the INES diffractometer at the ISIS facility provided essential data for numismatics research. A clear silver debasement occurring between the first and latter emissions has been traced, due to inflation processes which can be related with the increasing power of Roman Republic in the Cisalpine region. Moreover, compositional data enabled for the first time to identify internal evolutions inside typologies defined by numismatists. The silver loss has also been used to establish a relative chronology between different emissions. Other parameters such as texture index, residual strains and grain dimensions have been useful to understand technical aspects of minting procedures during Iron Age.