The true purity of Roman silver coinage was hidden by enriching the surfaces of the coins. The question investigated in this paper is whether Roman gold coins also were surfaced enriched.
Two non-destructive techniques were employed to do this: X-ray fluorescence (XRF) and a “newer” technique, muonic X-ray emission spectroscopy (μXES). For the latter, the momentum of the muons is controlled, allowing for the composition of the coin to be determined at various depths. The study shows there is no surface enrichment of the analyzed Roman gold coins.
Furthermore, the team shows that XRF and μXES return congruent results at the near-surface. This all supports the integrity of surface-level analyses of Roman gold coins.
The research team included George Alexander Green, Department of Classics and Ancient History, University of Warwick; Katsu Ishida, RIKEN Nishina Center, RIKEN, Wako, Saitama, Japan; Bethany V. Hampshire, Department of Physics, University of Warwick; Kevin Butcher, Department of Classics and Ancient History, University of Warwick; A. Mark Pollard, School of Archaeology, University of Oxford; and Adrian D.Hilliere, ISIS Neutron and Muon Facility, STFC Rutherford Appleton Laboratory, Didcot.
• Three Roman gold coins are analysed with muonic X-ray emission spectroscopy.
• The muons penetrated 0.4 mm into the coins totally non-destructively.
• The compositional results were congruent with those by X-ray fluorescence.
• The surfaces and cores of the coins had congruent results – no surface enrichment.
• This technique has great potential for the analysis of high-value museum objects.
Each coin was from the reign of a different Roman emperor. One came from the time of Hadrian (2nd century AD), one from the reign of Tiberius (1st century AD), and one from Julian II (4th century AD).