NIST researchers and their colleagues have demonstrated a method to distinguish century-old coins from fakes by imaging antique coins with beams of low-energy neutrons. Authenticating coins is critical because scientists rely on them to chronicle the economic, political, and scientific developments of nations. NIST researcher Daniel Hussey and his colleagues chose neutrons to examine two Korean coins—one minted in the 1800s, the other a replica—because these subatomic particles penetrate heavy metals, such as copper, iron, and lead, and interact strongly with hydrogen-bearing compounds that form as a byproduct of corrosion. The location and pattern of corrosion within the two coins, both composed of copper alloys, provided hallmarks for verifying their age. For instance, the neutron study revealed that in the authentic coin, corrosion had penetrated deep within the body, indicating that the degradation was a gradual process that occurred over many decades. In contrast, corrosion in the recently minted replica was mainly confined to the surface, consistent with rapid corrosion over a short time period. Neutron imaging methods can also assist conservation efforts by determining the amount and locations of corrosion in authentic coins, suggesting areas of the coins that need a protective coating, for example.

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