on-destructive determination of the silver content in roman coins dated to 308-311 a.d. by combined use of the PIXE-alpha, XRF and DPAA techniques

In the last years a non-destructive protocol of analysis, based on the combined use of the portable PIXE-alpha [1] and XRF spectrometers and of the new DPAA (Deep Protons Activation Analysis) method [2], was developed at the INFN-CNR LANDIS laboratory for studying the Roman folles dated to 294-333 A.D. belonging to the Misurata treasure (Lybia), one of the most important finding of coins in the Mediterranean Area. The main aim of the investigation was the determination of the silver content of the coins produced in different times and the study of the technique used to manufacture the folles. It is well known that the Roman folles were produced with a few microns silvered patina and a bronze core containing a lower quantity of silver. Therefore the association of non-destructive surface and in-depth techniques is necessary in order to investigated in a non-destructive way the different layers of the coins. The present paper discuss the results obtained from the analysis of 15 coins dated back to 308-311 A.D. produced by the mint of Carthago during the domination of the usurper L. Domitius Alexander. The analytical data obtained by the application of the above protocol of measurement allowed to make some considerations about the production of the folles in the Carthago area in this limited period of time.