Using Negative Muons as a Probe for Depth Profiling Silver Roman Coinage

• Published in: Heritage Vol. 2; no. 1; pp. 400 - 407
• Main Authors: Hampshire, Bethany, Butcher, Kevin, Ishida, Katsu, Green, George, Paul, Don, Hillier, Adrian
• Format: Journal Article
• Language: English
• Published: MDPI AG 01.03.2019
• Subjects: analysis; coin; elemental; muon; non-destructive; Roman; silver
• ISSN: 2571-9408; 2571-9408
• DOI: 10.3390/heritage2010028

Debasement of silver Roman coins is a well-known phenomenon and understanding the quality of ancient silver coinages can provide an idea about the underlying fiscal condition of the issuing states. These coins are made from a silver-copper alloy, the surfaces of which were deliberately enhanced at the mints by a process of surface-enrichment to give them the appearance of being made of pure silver. Therefore, any surface analysis would provide a composition of the silver-copper alloy that would not be representative of the original alloy from which the coin blank was made; the result would be too high in silver. However, the bulk of the sample, the interior, should provide a composition that is true to the original alloy. Elemental analysis using negative muons has been used to provide a depth dependent compositional, completely non-destructive analysis of a silver-copper alloy denarius of the empress Julia Domna datable to 211–217 CE. The composition of the coin, beyond the surface enrichment layer, is 51 ± 1.8 % copper and 49 ± 1.9% silver, taken at a muon depth of 402 ± 61 µm. The surface enrichment layer is approximately 190 µm thick.