X-ray diffraction or reflection?

  1. In x-ray diffraction , even though its reflection is happening , we call this as x ray diffraction. why is it so?? i don't know whether it has been discussed previously here.
     
  2. jcsd
  3. TumblingDice

    TumblingDice 463
    Gold Member

    Actually its diffraction that's happening. The terminology 'reflections' applies to the spots/patterns generated when x-rays diffract through a set of evenly spaced planes in a crystal. It's the mathematics of the monochromatic frequency of the x-rays and the angle of diffraction as the crystal is rotated. Diffraction patterns of spots/reflections are generated when the resulting wave patterns coincide and support each other.
     
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  4. does anybody have any other answer????
     
  5. Reflection and diffraction are really two different aspects of the same thing. The term reflection is used mostly for what happens at the surface of a homogenous medium. This does occur for x-rays, but only at very small angles, because the index of refractions is very very close to 1. Nevertheless the effect is used for things like space-based x-ray telescopes, focusing and harmonic rejection of synchrotron radiation, etc.

    http://en.wikipedia.org/wiki/X-ray_optics#Reflection

    Diffraction relies on the (constructive) interference of wavelets scattered from a period arrangement of objects. For x-rays that can be a crystal lattice, an artificial multilayer, a Fresnel lens structure, etc. Diffraction does not necessarily happen at a surface. In fact, Max von Laue and coworkers first discovered x-ray diffraction in a transmission geometry.

    http://www.iucr.org/__data/assets/pdf_file/0010/721/chap4.pdf, near page 40.
     
  6. TumblingDice

    TumblingDice 463
    Gold Member

    M Quack added good info and links for reflection and diffraction.

    Here's another wiki link directly to X-ray Crystallography:
    http://en.wikipedia.org/wiki/X-ray_crystallography

    The link has some more good stuff that directly addresses your question regarding, "why":
     
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  7. You (actually Wikipedia :wink:) are telling is that reflection ".... producing a diffraction pattern of regularly spaced spots known as reflections". But reflection is a physical phenomenon, so how cold you term spots as reflection??
     
  8. That is just nomenclature. At the Bragg condition the crystal "reflects" (should be diffracts!) x-rays, that's why it is known as Bragg reflection. This is the term that everybody uses, and I do not know of any better term. Get used to it.
     
  9. Okay.. Thank you.....
     
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