![]() IUCR Online Dictionary of Crystallography: This page contains the definition and direct derivation of Bragg's law, along with additional information about the order of the reflection, extinctions or systematic absences, and the influence of deformation SERC: This page contains a collection of links to Geochemical Analytical Instruments and techniques including Bragg's Law Stony Brook: This page contains information about Bragg's Law and diffraction HyperPhysics: This page contains information about Bragg's Law and the Bragg Spectrometer There are also good resources on the web: You can find basic information about x-ray diffraction in your favorite mineralogy text. Therefore, understanding Bragg's Law (nλ=2dsinθ) and the Laue equations is essential. As mentioned above, the physical principles that govern x-ray diffraction at high pressure are the same at low pressure. Synchrotron x-rays can be used for diffraction experiments conducted in both DAC and multi-anvil as well as the large opposed anvil device called the Paris-Edinburgh cell. Resolution is higher with lab sources but the intensity is much lower so the experimentalist must be patient as collection times are long. X-ray diffraction experiments can be conducted in DACs with both synchrotron and standard lab x-ray sources. Sufficiently bright X-rays can penetrate multi-anvil cell assemblies as well as diamond-anvil cells (DAC) and can produce patterns from just cubic microns worth of material. Typically an opposed anvil device called a Paris-Edinburgh apparatus is used for neutron diffraction. However, neutrons also require much more low Z-material (most earth materials fall into this category) to produce measurable diffraction. neutrons also interact with hydrogen which is nearly invisible to x-rays. Neutrons interact less with matter than electrons do so they can penetrate and diffract from high Z metal samples. Both neutrons and x-rays can be used in high pressure experiments. For example electron diffraction is an incredibly useful tool in transmission and scanning electron microscopy, but since electrons cannot penetrate any significant amount of solid, no one has figured out how to do electron diffraction during high pressure experiments. The only differences are related to the physical constraints placed by the high pressure apparatus. ![]() ![]() There is no fundamental difference between diffraction experiments conducted at high pressure and those at one atmosphere. By Pamela Burnley, University of Nevada Las Vegas Outline Introduction ![]()
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