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Bragg Diffraction

was discovered in a study by William Lawrence Bragg and William Henry Bragg.  They found that, for crystalline solids, X-ray light would be reflected yielding increased intensities only certain angles of reflection.   This phenomenon was determined to be a result of constructive interference.  Assuming a crystalline solid with spacing d between each molecule, and two parallel light sources: it can be determined that:

known as Bragg’s Law.  Constructive interference implies that two waves that are reflected by the material will stay in phase and produce a “Bragg Peak” only if the difference in their path length is equal to some multiple of the light’s wavelength.

Bragg Diffraction


occurs when X-rays strike an individual atom, and the photon thus causes the atom to emit electromagnetic radiation, usually in the form of another X-ray.  Note that the X-ray emitted as a result of fluorescence will occur multi-directionally whereas the X-rays from diffraction will propagate in more specific directions, usually in the exact opposite angle as the angle of incidence.

The CCD X-Ray Diffractometer/Florescence Instrument

used to produce the analyzed data sets was created by Keith Gendreau and his team from NASA. This device uses a Bremsstrahlung radiation source to shine a range of X-ray frequencies onto the sample being analyzed. This spectrum of frequencies allows diffraction patterns to be recorded on a CCD screen without the motion required by a monochromatic X-ray source. This reduction of motion, in addition to several other aspects, may allow this device to be used in future space missions. More information on the device may be found in the CXDRF Documentation.


Related Links Olin/NASA Home Olin College Goddard Space Center CXDRF Documentation Mineral Database X-spec Documentation

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