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MCAT Content / Light And Electromagnetic Radiation / Other Diffraction Phenomena X Ray Diffraction

Other diffraction phenomena, X-ray diffraction

Topic: Light And Electromagnetic Radiation

As X-rays have a very short wavelength, we can use crystalline solids as a natural 3D “diffraction grating” for X rays.

X-rays are electromagnetic radiation whose wavelengths are of the order of 1 Å (0.01 to 10 nanometers). Because x-ray wavelengths are about equal to atomic diameters, diffraction gratings cannot be constructed mechanically

X-ray crystallography is a method of determining the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information.

In an X-ray diffraction measurement, a crystal is rotated and bombarded with X-rays, producing a diffraction pattern of regularly spaced spots known as reflections. The two-dimensional images taken at different rotations are converted into a three-dimensional model of the density of electrons within the crystal.

Reflections in Diffraction Patterns: Each dot, called a reflection, in this diffraction pattern forms from the constructive interference of scattered X-rays passing through a crystal. The data can be used to determine the crystalline structure.

Key Points

• X- rays wavelengths are in the range of 0.01 to 10 nanometers.

• Crystalline solids can be used as a 3D diffraction grating for X-rays

Key Terms

crystalline solid: a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions

X-rays: electromagnetic radiation whose wavelengths are of the order of 1 Å (0.01 to 10 nanometers)

wavelengths: the measurement of the distance between two peaks or two troughs of a wave

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