Characterisation of silver pre-Roman coins from Northern Italy with neutron-based techniques

During the last two years, several pre-Roman coins from northern Italy have been analysed thanks to neutron-based techniques such as neutron diffraction (ND) and prompt gamma activation analysis (PGAA). This coinage is a collection of several series of silver coins, called drachmas, produced by different Celtic and non-Celtic tribes settled in northern Italy between the 4 th and the 1 st century B.C. They are all characterized by the imitation of the lion depicted on Massalia’s heavy drachm, whose different styles have been used by numismatists to group them in typo- logies. Many issues still remain unsolved, such as chronology, attributions and relationships within the emissions [1-2]. To provide new data for this study, a selection of specimens coming from different hoards and museum collections, re- presentative of different emissions, has been analyzed with non-destructive neutron based techniques, which allowed the problem of the silver surface enrichment [3] to be overcome. We performed time-of-flight neutron diffraction measurements with the INES diffractometer [4] at the ISIS facility (Rutherford Appleton Laboratory, UK) on coins coming from the Biandrate (NO), Casale Monferrato (AL) and Serra Riccò (GE) hoards and from some numismatics collections in Turin. The analysis of dif- fraction patterns has been carried out with the GSAS software to determine phase weight fractions through Rietveld refinement. Other pre-Romans coins, kept at the Hungarian National Museum [5], have been measured at the PGAA station [6] of the Budapest Neutron Centre. The possibility to analyse these coins has been a unique chance, because of the richness of the collection and the presence of several typologies not previously analysed. The results obtained on around 100 coins show a clear silver debasement occurring among the first and latter drachmas emissions, due to inflation processes which can be related with the increasing economic power of the Roman republic in the Po valley. The silver loss can be also used to establish a relative chronology between the different emissions, in agreement with the few dating data available from archaeological research. These results are also providing new fundamental elements for the study of metrological relationships with the contemporary Roman republican currency. Finally, a comparison between ND and PGAA measurements will be presented, providing results both on standards and coins, in order to combine the results obtained with the two techniques. Acknowledgements: This project has been supported by the Cooperation Agree- ment no. 06/20018 between CNR and STFC. The financial support by CHARISMA Grant Agreement n. 228330 is grate- fully acknowledged. We kindly acknowledge Dr. M. Torbágyi for the loan of coins of the Hungarian National Museum and Dr. A. Guerrini for those from the Armeria Reale in Turin. Bibliography [1] Pautasso, A., 1966. Le monete preromane dell’Italia settentrionale, Sibrium, 7: 1-162. [2] Arslan, E.A., 1995. La monetazione celtica cisalpina. Un nuovo quadro generale, Sibrium, 22: 179-215. [3] Beck, L., Bosonnet, S., Réveillon, S., Eliot, D., Pilon, F., 2004. Silver surface enrichment of silver-copper alloys: a limitation for the analysis of ancient silver coins by surface techniques, Nuclear Instruments and Methods in Physics Research B, 226: 153-162. [4] Grazzi, F., Celli, M., Siano, S., Zoppi, M., 2007. Preliminary results of the Italian neutron experimental station INES at ISIS: Archaeometric applications, Il Nuovo Cimento C, 30: 59-65. [5] Arslan, E.A., 1991-1992. Le monete padane preromane a Budapest, Numizmatikai Közlöny, XC-XCI: 9-33. [6] Révay, Zs., Belgya, T., Kasztovszky, Zs., Weil, J.L., Molnár, G.L., 2004. Cold neutron PGAA facility at Budapest, Nuclear Instruments and Methods in Physics Research B, 213: 385-388.