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Structure determination by X-ray crystallography
is a technique in crystallography
in which the pattern produced by the diffraction
through the closely spaced lattice of atoms
in a crystal
is recorded and then analyzed to reveal the nature of that lattice. This generally leads to an understanding of the material and molecular structure of a substance. The spacing in the crystal lattice can be determined using Bragg's law
. The electrons
that surround the atoms, rather than the atomic nuclei
themselves, are the entities that physically interact with the incoming X-ray photons
. This technique is widely used in chemistry
to determine the structures of an immense variety of molecules, including inorganic compounds, DNA
, and proteins
. X-ray diffraction is commonly carried out using single crystals of a material, but if these are not available, microcrystalline powdered samples
may also be used, although this requires different equipment, gives less information, and is much less straightforward.
Did you know...
Mock mirage of the setting sun
- ...that your watch would run slower when orbiting a black hole than it would on Earth?
- ...that Aristotle's ideas of physics held that because an object could not move without an immediate source of energy, arrows created a vacuum behind them that pushed them through the air.
- ...that nuclear fusion reactions are probably occurring at or above the sun's photosphere; it is a process called solar surface fusion.
Artist's depiction of the WMAP
satellite measuring the Cosmic Microwave Background Radiation
to help scientists understand the Big Bang
- ...that neutron stars are so dense that a teaspoonful (5 mL) would have ten times the mass of all human world population?
- ...that every year, the Moon moves 3.82 cm away from Earth?
- ...that Neptune was discovered by its gravitational pull on Uranus?
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An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the early 1800s, was the first practical electric light. It was widely used starting in the 1870s for street and large building lighting until it was superseded by the incandescent light in the early 20th century. It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II.
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