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. 2021 Aug 3;7(8):129.
doi: 10.3390/jimaging7080129.

Phase Composition and Its Spatial Distribution in Antique Copper Coins: Neutron Tomography and Diffraction Studies

Bulat Bakirov  1   2 , Irina Saprykina  1   3 , Sergey Kichanov  1 , Roman Mimokhod  3 , Nikolay Sudarev  3 , Denis Kozlenko  1
Affiliations

Phase Composition and Its Spatial Distribution in Antique Copper Coins: Neutron Tomography and Diffraction Studies

Bulat Bakirov et al. J Imaging. .

Abstract

The chemical and elementary composition, internal arrangement, and spatial distribution of the components of ancient Greek copper coins were studied using XRF analysis, neutron diffraction and neutron tomography methods. The studied coins are interesting from a historical and cultural point of view, as they are "Charon's obol's". These coins were discovered at the location of an ancient Greek settlement during archaeological excavations on the "Volna-1" necropolis in Krasnodar Region, Russian Federation. It was determined that the coins are mainly made of a bronze alloy, a tin content that falls in the range of 1.1(2)-7.9(3) wt.%. All coins are highly degraded; corrosion and patina areas occupy volumes from ~27 % to ~62 % of the original coin volumes. The neutron tomography method not only provided 3D data of the spatial distribution of the bronze alloy and the patina with corrosion contamination inside coin volumes, but also restored the minting pattern of several studied coins. Taking into account the obtained results, the origin and use of these coins in the light of historical and economic processes of the Bosporan Kingdom are discussed.

Keywords: Bosporan coins; copper coins; neutron imaging; neutron tomography.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
An example of the neutron diffraction patterns of coin MP467, for which the experimental points and fitted profile are shown. Tick marks are the calculated positions of the Bragg peaks of the copper, copper oxide and copper chloride phases. The most intense diffraction peaks of those phases with hkl-indexes are labeled.
Figure 2
Figure 2
Diagram of the tin content in the studied bronze coins. The results were obtained from an analysis of neutron diffraction data. The average error in determining the tin content of bronze alloy does not exceed 0.3 wt.%.
Figure 3
Figure 3
The 3D models after tomographic reconstruction and several transversal slices of the 3D models of the coins. The rainbow-like scale of neutron attenuation coefficients is shown. The regions with lower neutron attenuation coefficient can be attributed to copper–tin alloy areas, while the areas corresponding to high neutron attenuation coefficients are assumed to be corrosive contamination and patina materials. The dimensions of the reconstructed models correspond to the sizes of the coins shown in Table 1.
Figure 4
Figure 4
The examples of reconstructed patterns on the surface of several coins from the neutron tomography data. (a) The MP468 coin with patterns of a bow, arrow and the inscription “IIAN”. (b) The reconstructed view of the “Twenty-ray star” on the MP465 coin. A photo of a similar coin from the catalog [36,37].
See this image and copyright information in PMC

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