Silver surface enrichment in ancient coins studied by micro-PIXE

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 2013-07, Vol.306, p.241-244
• Main Authors: Ager, F.J., Moreno-Suárez, A.I., Scrivano, S., Ortega-Feliu, I., Gómez-Tubío, B., Respaldiza, M.A.
• Format: Article
• Language: English
• Subjects: Alloys; Cross sections; Enrichment; Nondestructive testing; Nuclear microprobe; PIXE; Roman; Roman silver coins; Silver; Silver enrichment; Silver–copper alloys; X-ray fluorescence
• ISSN: 0168-583X; 1872-9584
• DOI: 10.1016/j.nimb.2012.12.037

The surface enrichment of archeological silver–copper alloys, either intentional or due to corrosion processes, has been known for many years. The most used non-destructive techniques, such as particle-induced X-ray emission (PIXE) and X-ray fluorescence (XRF) are surface techniques, with penetration depths typically ranging from a few microns to a few tens of microns. Therefore, these techniques could produce results which are not representative of the bulk composition of the alloy. In order to gain insight into the silver enrichment process and the effects on the data obtained with these techniques, a set of silver roman denarii were cross sectioned and analyzed at the Centro Nacional de Aceleradores micro-PIXE facility. Elemental maps show silver surface enriched layers up to 250μm thick. Besides, silver-enriched surface layers are not found for alloys with 96–98wt.% Ag.