X-ray Diffraction
Introduction
X-ray diffraction (XRD) is a X-ray-based technique used in crystallography to determine the atomic and molecular structure of a crystal. The X-ray beam is diffracted by the crystal lattice, and the resulting diffraction pattern can be used to deduce the crystal's structure.
Principle of X-ray Diffraction
The principle of X-ray diffraction is based on the Bragg's law, which states that diffraction can occur whenever the scattered waves interfere constructively. This happens when the path difference between the scattered waves is equal to an integer multiple of the wavelength. The crystal lattice acts as a three-dimensional diffraction grating for the incident X-rays, leading to a complex diffraction pattern that can be analyzed to reveal the crystal's structure.
X-ray Generation and Detection
X-rays are generated by an X-ray tube, which uses a high voltage to accelerate electrons towards a metal target. The high-energy electrons dislodge inner shell electrons in the metal atoms, and the resulting vacancies are filled by electrons from higher energy levels. This process, known as characteristic X-ray production, leads to the emission of X-rays with specific energies related to the atomic structure of the metal target.
The diffracted X-rays are detected by a X-ray detector, which converts the X-ray photons into an electrical signal that can be processed and analyzed. The type of detector used can vary depending on the specific requirements of the X-ray diffraction experiment.
Applications of X-ray Diffraction
X-ray diffraction has a wide range of applications in various fields. In material science, it is used to determine the crystal structure of materials, to identify unknown substances, to measure the size and shape of crystallites, and to study defects and impurities in crystals. In biology, X-ray diffraction is used to determine the structure of large biomolecules such as proteins and nucleic acids. In geology, it is used to identify minerals and to study the crystal structure of rocks.