NIST Team Uses Neutron Beams to Authenticate Historic Coins and Spot Fakes

Imaging antique coins with beams of low-energy neutrons, researchers at the National Institute of Standards and Technology (NIST) and their colleagues have demonstrated a method to distinguish century-old coins from fakes. Authenticating coins is critical because scientists rely on them to chronicle the economic, political, and scientific developments of nations.

NIST researchers Youngju Kim, Daniel Hussey, and their 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.

The team employed two complementary imaging techniques. One of the methods, known as neutron tomography, uses a beam of neutrons to take a series of two-dimensional images of an object from different perspectives as the object rotates. Just as in an X-ray CT scan, these two-dimensional snapshots are combined to reveal the three-dimensional structure of the coins.

The other method, known as neutron grating interferometry, records neutrons scattered at small angles and homes in on microstructures, such as pitting and pores within the coins, that are signs of corrosion.

In the authentic coin, the researchers found that 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.

The team also used neutron grating interferometry to examine the size of pores within the coins, which provided another method to distinguish between the historic coin and the fake. Pores are created when coins buried in soil or exposed to moisture chemically interact with their environment. The interaction causes metallic compounds to leach out of the coins, leaving behind millimeter-sized holes.

As time goes on, however, compounds in the environment begin to penetrate the coins. These compounds, which includes corrosion byproducts such as copper carbonates, sulfates, and chlorides, pack together and fill the pores, diminishing their size. Indeed, the imaging revealed that the historic coin, which was exposed to its environment for a much longer period of time, had much smaller pores, only micrometers to nanometers in size, compared to the millimeter-sized pores in the replica.

The researchers, which include scientists from the University of Maryland in College Park, the University of Tennessee in Knoxville, Pusan National University in Busan, South Korea, and the Korea National University of Heritage in Buyeo, reported their work online in Scientific Reports on April 28.

With their initial study a success, the scientists plan to continue their work with a larger supply of Korean coins. They emphasize that their technique can be applied to a broader range of metallic artifacts from a diversity of cultures.

Neutron-imaging methods can also assist conservation efforts by determining the amount and locations of corrosion in authentic coins. The imaging could suggest areas of the coins that need a protective coating, for example.

The team used the NIST research reactor in Gaithersburg, Md., to generate the neutron beams. With that facility closed until 2026, the researchers are continuing their work with a research reactor in South Korea.

Paper: Y. Kim, M. C. Daugherty, D. S. Hussey, J. M. LaManna, D. L. Jacobson, C. M. Wolf, P. A. Kienzle, D. Kim, S. W. Lee, M. Han, H. Choo, J. Kim, T. Kim. Application of neutron grating interferometry and tomography to study ancient Korean copper coins. Scientific Reports, published online April 28, 2025, vol. 15, Article number: 14848. https://doi.org/10.1038/s41598-025-99235-x