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The longest wavelength x-ray that can undergo Bragg diffraction in a crystal for a given family of planes of spacing d is

  1. d/4
  2. d/2
  3. d
  4. 2d
  5. 4d

Atomic}Bragg Diffraction

Recall the Bragg Diffraction dispersion relation,

thus the maximal wavelength \lambda would be 2d, choice (D). (One can derive that even if one does not remember the formula. Consider two lattice planes. View them from the side so that they appear as two parallel lines. A wave would hit the both planes at, say, an angle \theta from the normal. The wave that reflects off the bottom lattice will have to travel an extra distance, relative to the wave hitting the top plane, equal to 2d\sin\theta.)

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pam d
2011-09-27 14:21:19
Yeah, like gt2009, I would just like to reiterate how important it is that the angle in the Bragg relation is the glancing angle, NOT the angle from the normal.NEC
2009-06-14 13:31:29
\theta is the glancing angle, not the angle from the normal (or just use cosine instead of sine).NEC

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