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郭可信. X射线衍射的发现[J]. 物理, 2003, 32(07).
引用本文: 郭可信. X射线衍射的发现[J]. 物理, 2003, 32(07).
The discovery of X-ray diffraction[J]. PHYSICS, 2003, 32(07).
Citation: The discovery of X-ray diffraction[J]. PHYSICS, 2003, 32(07).

X射线衍射的发现

The discovery of X-ray diffraction

  • 摘要: 简单介绍了埃瓦尔德(Ewald P P)、劳厄(von Laue M)和布拉格父子(Bragg W H及Bragg W L)在1912年发现X射线衍射方面的贡献.1911年埃瓦尔德在索末菲的指导下在慕尼黑大学从事博士论文研究,劳厄在与他的讨论中了解到晶格的平移周期与X射线的波长属于同一量级,因此想到在二维光栅的两个衍射方程组中再加一个类似的方程,就可以描述X射线在三维晶体中的衍射.在此假设的指导下,Friedrich W和Knipping P在1912年4月开始用CuSO4后来用闪锌矿(立方ZnS)进行实验,很快就得到X射线衍射的证据.这不但证明了X射线的波动性,还确定了晶体的三维周期性.老布拉格在1912年夏得知这个消息,与他儿子小布拉格一道尝试用X射线的粒子性解释它,并由小布拉格在剑桥大学重复这个实验.根据衍射斑点的椭圆形状和从Pope与Barlow那里学到的晶格理论(由此得知ZnS具有面心立方晶格),小布拉格将X射线在晶体中的衍射看作是X射线从一些晶格平面的反射,从而推导出著名的布拉格方程.布拉格父子开拓了X射线晶体结构分析这门新兴学科,从简单的无机化合物和矿物,逐渐发展到有机化合物和生物大分子.劳厄和布拉格父子分别强调慕尼黑和剑桥的优良科学环境对发现X射线衍射的重要性.鉴于埃瓦尔德在发现X射线衍射的作用及他后来在倒易格子及动力学衍射理论方面的贡献,不少晶体学家认为他也应获得诺贝尔物理奖.

     

    Abstract: The contributions of P.P. Ewald, M. von Laue, W.H. Bragg (father) and W.L. Bragg (son) to the discovery of X-ray diffraction in 1912 are discussed. While discussing Ewald‘s Ph.D. thesis supervised by Sommelfeld in Munich, Laue learnt of the translation periodicity in a crystal lattice, which was about the same order of magnitude as the wavelength of X-rays. This gave him the idea that X-ray diffraction in a crystal could be treated by adding one more diffraction equation to the two-dimensional diffraction of a cross-grid pattern. Under the guidance of this hypothesis, Friedrich and Knipping carried out X-ray diffraction experiments in April 1912, first on orthorhombic CuSO4 and later on cubic ZnS, and soon found definite evidence of X-ray diffraction. This proved not only the wave nature of X-rays but also the three-dimensional periodicity of a crystal. After receiving this news in the summer of 1912 in Leeds, W.H. Bragg tried to explain it by the particle theory of X-rays, while his son W.L. Bragg carried out similar diffraction experiments in Cambridge. Based upon the elliptical shape of the diffraction spots and the crystal lattice theory learnt from Pope and Barlow, W.L. Bragg came to the conclusion that X-ray diffraction in a crystal could be treated as reflection from parallel lattice planes, and hence derived the famous Bragg equation. The Braggs then developed a new branch of science, namely the crystal structure analysis of simple inorganic compounds, minerals, organic molecules, and biological macromolecules. Both Laue and the Braggs acknowledge the importance of the very favorable environment in Munich and Cambridge that led to the discovery of X-ray diffraction. In view of the important contributions of Ewald to the discovery of X-ray diffraction, his reciprocal lattice theory and later his dynamical diffraction theory, many crystallographers consider that he should also have received the Nobel prize.

     

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