Pub Date : 2020-07-23DOI: 10.1093/oso/9780198851875.003.0002
B. Cantor
The diffraction of X-rays is used as the main method for determining the atomic and molecular structures of inorganic and biological materials. The basic law of diffraction was discovered by Lawrence Bragg when he was a student at Cambridge University and he was just 22 years old. Bragg’s law explains how the angle of a diffracted X-ray beam varies with the wavelength of the X-rays and the spacing of the atoms and molecules in the material. This chapter examines the way X-rays are generated and scattered by electrons, atoms and crystals; the use of structure factors and Fourier transforms to calculate the intensity of the scattered X-rays; and the effect of using electrons or neutrons instead of X-rays. Bragg was born and brought up in Adelaide in Australia. He discovered Bragg’s law with the help of his father, William, after they had moved to England. Lawrence was a Professor at Manchester University, Cambridge University, and the Royal Institution; contributed to the development of range-finding, asdic, and sonar during the First and Second World Wars; and supervised Crick and Watson when they discovered the structure of DNA.
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Pub Date : 2020-07-23DOI: 10.1093/oso/9780198851875.003.0001
Brian Cantor
Most solid materials are crystalline, with their component atoms and molecules arranged in regular arrays throughout space. The French scientist Auguste Bravais showed that there are only 14 different ways of doing this, called the Bravais lattices, each with different symmetry. In other words, there is a Bravais equation for the number of different lattices: N L = 14. This chapter examines the relationship between Bravais lattices, crystal systems and symmetry groups, the use of Miller indices to describe crystal planes and directions, and the use of stereograms to describe crystal orientations. Bravais’ early life in the Ardèche in France is described, along with his exciting career during and after the French Revolution: as an officer in the French navy during the Barbary wars; as an explorer in North Africa, the Arctic and the Alps, notably leading the second scientific ascent of Mont Blanc; and as an environmental, geophysical and crystallographic scientist.
大多数固体材料都是晶体状的，它们的组成原子和分子在空间中以规则的排列排列。法国科学家奥古斯特·布拉维(Auguste Bravais)指出，只有14种不同的方法可以做到这一点，称为布拉维格(Bravais lattice)，每种方法都有不同的对称性。换句话说，有一个关于不同格数的Bravais方程:N L = 14。本章研究了Bravais晶格、晶体系统和对称群之间的关系，使用Miller指标来描述晶体的平面和方向，以及使用立体图来描述晶体的取向。书中描述了布拉维早年在法国ard区的生活，以及他在法国大革命期间和之后令人兴奋的职业生涯:在巴巴里战争期间担任法国海军军官;作为北非、北极和阿尔卑斯山的探险家，领导了勃朗峰的第二次科学攀登;作为一名环境、地球物理和晶体学科学家。
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