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Laue diffraction
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Laue diffraction

physics
Also known as: Laue method
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Key People:
Max von Laue
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X-ray diffraction
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Laue diffraction, in X-rays, a regular array of spots on a photographic emulsion resulting from X-rays scattered by certain groups of parallel atomic planes within a crystal. When a thin, pencil-like beam of X-rays is allowed to impinge on a crystal, those of certain wavelengths will be oriented at just the proper angle to a group of atomic planes so that they will combine in phase to produce intense, regularly spaced spots on a film or plate centred around the central image from the beam, which passes through undeviated. Laue diffraction, first detected by Max von Laue, a German physicist, is invaluable for crystal analysis.

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X-ray diffraction
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Bragg diffraction Proteins and X-ray diffraction
Bragg diffraction
Bragg diffraction Bragg diffraction. Waves 1 and 2, in phase with each other, glance off atoms A and B of a crystal that has a separation distance d between its atomic, or lattice, planes. The reflected (glancing) angle θ, as shown by experiment, is equal to the incident angle θ. The condition for the two waves to stay in phase after both are reflected is that the path length CBD be a whole number (n) of wavelengths (λ), or nλ. But, from geometry, CB and BD are equal to each other and to the distance d times the sine of the reflected angle θ, or d sin θ. Thus, nλ = 2d sin θ, which is the Bragg law. As may be seen from the diagram, when n = 2, there is only one wavelength along path CB; also, the reflected angle will be smaller than that for, say, n = 3. Waves reflected through an angle corresponding to n = 1 are said to be in the first order of reflection, the angle corresponding to n = 2 is the second order, and so on. For any other angle (corresponding to fractional n), the reflected waves will be out of phase and destructive interference will occur, annihilating them.

X-ray diffraction

physics
Also known as: X-ray diffraction analysis
Written and fact-checked by
The Editors of Encyclopaedia Britannica
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.
The Editors of Encyclopaedia Britannica
Article History
Proteins and X-ray diffraction
Proteins and X-ray diffractionX-ray diffraction pattern of a crystallized enzyme.

X-ray diffraction, phenomenon in which the atoms of a crystal, by virtue of their uniform spacing, cause an interference pattern of the waves present in an incident beam of X-rays. The atomic planes of the crystal act on the X-rays in exactly the same manner as does a uniformly ruled diffraction grating on a beam of light. A beam of X-rays contacts a crystal with an angle of incidence θ. It is reflected off the atoms of the crystal with the same angle θ. The X-rays reflect off atomic planes in the crystal that are a distance d apart. The X-rays reflecting off two different planes must interfere constructively to form an interference pattern; otherwise, the X-rays would interfere destructively and form no pattern. To interfere constructively, the difference in path length between the beams reflecting off two atomic planes must be a whole number (n) of wavelengths (λ), or nλ. This leads to the Bragg law nλ = 2d sin θ. By observing the interference pattern, the internal structure of the crystal can be deduced. See also Bragg law; Laue diffraction pattern.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.
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