使用中子發現假古董硬幣

樣品中氫的存在通常是中子散射實驗中的壞事

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.

在中子散射實驗中，氫的存在通常是一件壞事，但是現在美國的研究人員將桌子上的桌子轉移到了最輕的元素上，並將其用於發現假古董硬幣。

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.

相對於其他類型的電磁輻射，中子可以在不被吸收的情況下傳播材料的距離相對較大。該特性可用於探測材料的整體特性，尤其是當中子的波長與材料中的原子分離相當時。在這些波長下，可以通過原子散射中子，並且可以測量散射波的相對相和幅度，以重建材料結構的圖像。

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，在生物結構測定中，蛋白質，DNA和其他生物分子通常放在溶液中，並使用所得的散射數據來確定溶液中分子的3D結構。然而，氫-1核（質子）在隨機方向上散射中子非常好，這會產生嘈雜的背景信號。因此，在將生物樣品置於中子束中之前，通常“將生物樣品“氘化” - 用氘代替氫。

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

但是，確實存在特殊情況，例如，這種不連貫的氫散射可能很有用 - 例如，測量樣品的水含量。

Surfeit of hydrogen

氫的過度

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.

現在，美國和韓國的研究人員已經使用了中子束來區分真正的古董硬幣和假貨。該技術依賴於真正的硬幣遭受腐蝕的事實，導致硬幣內包含含氫的化合物。

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.

在科羅拉多州國家標準技術研究所（NIST）的Youngju Kim和Daniel Hussey的帶領下，該團隊通過單個硬幣發射了平行的中子光束（見圖）。顆粒輕鬆地通過硬幣的原始金屬傳播，但往往會被富含氫的腐蝕夾雜物散射。這會在硬幣後面的中子敏感屏幕上創建高強度區域的2D模式。硬幣可以旋轉並拍攝一系列圖像。然後，研究人員使用計算機斷層掃描來創建一個3D圖像，顯示硬幣的腐蝕區域。

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.

該團隊使用這種中子斷層掃描技術來檢查地道的19世紀硬幣，該硬幣是從沉船中回收的，以及眾所周知的複製品的硬幣。儘管兩枚硬幣都有表面腐蝕，但腐蝕比在復製品中更深地擴展到了真實硬幣的大部分。

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.

研究人員還使用了一種稱為中子光柵干涉法的單獨技術來表徵硬幣表面中的孔。通常在被埋葬或淹沒的硬幣表面上觀察到毛孔。真實的古董硬幣將被埋葬或淹沒，而復制硬幣將被埋葬或淹沒，以使其看起來更真實。

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.

中子光柵干涉測量指標著眼於中子的小角度散射，並著重於大小從約1 nm到1微米的結構。

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.

該小組發現，正宗的硬幣的毛孔比複製硬幣的毛孔更小，後者以更大的（毫米尺度）的毛孔為主。

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.

這一觀察結果是可以預期的，因為當硬幣被埋葬或淹沒時，化學反應會導致金屬從其表面浸出，從而產生毫米尺寸的孔。然而，隨著時間的流逝，進一步的化學反應會導致腐蝕副產品（例如銅碳酸鹽）填充毛孔。結果是，較舊的正宗硬幣中的孔小於較新的複制硬幣中的孔。

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.

該團隊現在計劃擴大研究，以包括更多韓國硬幣和其他金屬人工製品。這些技術也可以用於查明古董硬幣中的腐蝕損傷，從而可以使用塗層保護這些區域。

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.

除了對硬幣收藏家和經銷商的重要性外，還具有驗證硬幣時代的能力，這對歷史學家和經濟學家來說是感興趣的 - 他們在研究中使用硬幣的存在。

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.

這項研究是使用馬里蘭州NIST研究反應堆的中子進行的。該設施定於2026年關閉，因此該團隊計劃使用韓國的中子來源繼續調查。

The research is described in Scientific Reports.

該研究在科學報告中進行了描述。