使用中子发现假古董硬币

样品中氢的存在通常是中子散射实验中的坏事

The presence of hydrogen is usually a bad thing in neutron scattering experiments, but now researchers in the US have turned the tables on the lightest element and used it to spot fake antique coins.

在中子散射实验中，氢的存在通常是一件坏事，但是现在美国的研究人员将桌子上的桌子转移到了最轻的元素上，并将其用于发现假古董硬币。

Relative to other types of electromagnetic radiation, neutrons can travel relatively large distances in materials without being absorbed. This property is useful for probing the bulk properties of materials, especially when the neutrons’ wavelengths are on par with the atomic separations in a material. At these wavelengths, neutrons can be scattered by atoms in a material, and the relative phases and amplitudes of the scattered waves can be measured to reconstruct images of the material’s structure.

相对于其他类型的电磁辐射，中子可以在不被吸收的情况下传播材料的距离相对较大。该特性可用于探测材料的整体特性，尤其是当中子的波长与材料中的原子分离相当时。在这些波长下，可以通过原子散射中子，并且可以测量散射波的相对相和幅度，以重建材料结构的图像。

For example, in biological structure determination, proteins, DNA and other biomolecules are usually placed in a solution and the resulting scattering data are used to determine the 3D structure of the molecule in the solution. However, hydrogen-1 nuclei (protons) are very good at scattering neutrons in random directions, which creates a noisy background signal. For this reason, biological samples are usually “deuterated” – replacing hydrogen with deuterium – before they are placed in a neutron beam.

例如，在生物结构测定中，蛋白质，DNA和其他生物分子通常放在溶液中，并使用所得的散射数据来确定溶液中分子的3D结构。然而，氢-1核（质子）在随机方向上散射中子非常好，这会产生嘈杂的背景信号。因此，在将生物样品置于中子束中之前，通常“将生物样品“氘化” - 用氘代替氢。

Special cases do exist, however, where this incoherent scattering of hydrogen can be useful – measuring the water content of samples, for instance.

但是，确实存在特殊情况，例如，这种不连贯的氢散射可能很有用 - 例如，测量样品的水含量。

Surfeit of hydrogen

氢的过度

Now, researchers in the US and South Korea have used a neutron beam to differentiate between genuine antique coins and fakes. The technique relies on the fact that the genuine coins have suffered corrosion that has resulted in the inclusion of hydrogen-bearing compounds within the coins.

现在，美国和韩国的研究人员已经使用了中子束来区分真正的古董硬币和假货。该技术依赖于真正的硬币遭受腐蚀的事实，导致硬币内包含含氢的化合物。

Led by Youngju Kim and Daniel Hussey at the National Institute of Standards and Technology (NIST) in Colorado, the team fired a parallel beam of neutrons through individual coins (see figure). The particles travel with ease through a coin’s original metal, but tend to be scattered by the hydrogen-rich corrosion inclusions. This creates a 2D pattern of high and low intensity regions on a neutron-sensitive screen behind the coin. The coin can be rotated and a series of images taken. Then, the researchers used computed tomography to create a 3D image showing the corroded regions of a coin.

在科罗拉多州国家标准技术研究所（NIST）的Youngju Kim和Daniel Hussey的带领下，该团队通过单个硬币发射了平行的中子光束（见图）。颗粒轻松地通过硬币的原始金属传播，但往往会被富含氢的腐蚀夹杂物散射。这会在硬币后面的中子敏感屏幕上创建高强度区域的2D模式。硬币可以旋转并拍摄一系列图像。然后，研究人员使用计算机断层扫描来创建一个3D图像，显示硬币的腐蚀区域。

The team used this neutron tomography technique to examine an authentic 19th century coin that was recovered from a shipwreck, and on a coin that is known to be a replica. Although both coins had surface corrosion, the corrosion extended much deeper into the bulk of the authentic coin than it did in the replica.

该团队使用这种中子断层扫描技术来检查地道的19世纪硬币，该硬币是从沉船中回收的，以及众所周知的复制品的硬币。尽管两枚硬币都有表面腐蚀，但腐蚀比在复制品中更深地扩展到了真实硬币的大部分。

The researchers also used a separate technique called neutron grating interferometry to characterise the pores in the surfaces of the coins. Pores are commonly observed on the surface of coins that have been buried or submerged. Authentic antique coins will be buried or submerged, whereas replica coins will be buried or submerged to make them look more authentic.

研究人员还使用了一种称为中子光栅干涉法的单独技术来表征硬币表面中的孔。通常在被埋葬或淹没的硬币表面上观察到毛孔。真实的古董硬币将被埋葬或淹没，而复制硬币将被埋葬或淹没，以使其看起来更真实。

Small-angle scattering

小角度散射

Neutron grating interferometry looks at the small-angle scattering of neutrons from a sample and focuses on structures that range in size from about 1 nm to 1 micron.

中子光栅干涉测量指标着眼于中子的小角度散射，并着重于大小从约1 nm到1微米的结构。

The team found that the authentic coin had many more tiny pores than the replica coin, which was dominated by much larger (millimetre scale) pores.

该小组发现，正宗的硬币的毛孔比复制硬币的毛孔更小，后者以更大的（毫米尺度）的毛孔为主。

This observation was expected because when a coin is buried or submerged, chemical reactions cause metals to leach out of its surface, creating millimetre-sized pores. As time progresses, however, further chemical reactions cause corrosion by-products such as copper carbonates to fill in the pores. The result is that the pores in the older authentic coin are smaller than the pores in the newer replica coin.

这一观察结果是可以预期的，因为当硬币被埋葬或淹没时，化学反应会导致金属从其表面浸出，从而产生毫米尺寸的孔。然而，随着时间的流逝，进一步的化学反应会导致腐蚀副产品（例如铜碳酸盐）填充毛孔。结果是，较旧的正宗硬币中的孔小于较新的复制硬币中的孔。

The team now plans to expand its study to include more Korean coins and other metallic artefacts. The techniques could also be used to pinpoint corrosion damage in antique coins, allowing these areas to be protected using coatings.

该团队现在计划扩大研究，以包括更多韩国硬币和其他金属人工制品。这些技术也可以用于查明古董硬币中的腐蚀损伤，从而可以使用涂层保护这些区域。

As well as being important to coin collectors and dealers, the ability to verify the age of coins is of interest to historians and economists – who use the presence of coins in their research.

除了对硬币收藏家和经销商的重要性外，还具有验证硬币时代的能力，这对历史学家和经济学家来说是感兴趣的 - 他们在研究中使用硬币的存在。

The study was done using neutrons from NIST’s research reactor in Maryland. That facility is scheduled to close in 2026 so the team plans to continue its investigation using a neutron source in South Korea.

这项研究是使用马里兰州NIST研究反应堆的中子进行的。该设施定于2026年关闭，因此该团队计划使用韩国的中子来源继续调查。

The research is described in Scientific Reports.

该研究在科学报告中进行了描述。