Bragg condition reflection vs. diffraction

In summary, the Bragg condition for constructive interference in crystal diffraction is based on the assumption of reflection, even though x-rays actually diffract on the crystal. This is because the combined scattering of x-rays from crystal planes can be looked upon as reflections, and at certain glancing angles, these reflections are in phase and produce maximum intensity. This allows us to use Bragg's equation to calculate interplanar spacing.
  • #1
frater
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I've been asking myself this question that is not entirely clear to me: the Bragg condition used to describe the constructive interference of waves on a crystal is based on the assumption of reflection. However, x-rays diffract on a crystal rather than reflect, so theoretically there is always some ray which refracts at an angle that would yield a path difference just right to produce constructive interference. Why then does the Bragg condition based on a reflection model work?

Thanks for any answers!
 
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  • #2
You are right...but that takes you back to Laue refraction equation, a few months before Bragg's equation and its more complicated.
It was Bragg's assumption to treat diffraction as reflection from lattice planes which led him to the simpler well known condition.
 
  • #3
Well ok, I understand that the full description the underlying physics is given by the Laue equations. But what I don't understand is why does the Bragg condition work at all since it is based on an "unphysical" assumption of reflection. Is there some simple reasoning I am missing why the reflection description, even if not correct, nevertheless accurately produces the condition for constructive diffraction?
 
  • #4
"it is based on an "unphysical" assumption of reflection"

Not like that...There is real reflection, in the sense that the combined scattering of x-rays from crystal planes can be looked upon as reflections from these planes.

At certain glancing angles, these reflections are in phase and produce maximum intensity. By measuring theses angles for different set of planes, knowing the wavelength, we can calculate interplanar spacing from Bragg's eq.
 

FAQ: Bragg condition reflection vs. diffraction

1. What is the Bragg condition for reflection vs. diffraction?

The Bragg condition states that for a diffraction pattern to be produced, the wavelength of the incident radiation must be equal to twice the spacing between the planes of atoms in the crystal lattice.

2. How does the Bragg condition differ for reflection and diffraction?

In reflection, the Bragg condition still applies, but it is used to determine the angle at which the incident radiation will be reflected from the crystal lattice. In diffraction, the Bragg condition is used to determine the angles at which the diffraction peaks will be produced.

3. Can the Bragg condition be applied to any type of crystal lattice?

Yes, the Bragg condition can be applied to any crystal lattice, as long as it has regularly spaced planes of atoms.

4. How does the Bragg condition affect the intensity of the diffraction peaks?

The Bragg condition plays a crucial role in determining the intensity of the diffraction peaks. When the Bragg condition is satisfied, the diffraction peaks will be at their maximum intensity. If the Bragg condition is not satisfied, the diffraction peaks will be weaker or may not appear at all.

5. Is the Bragg condition the only factor that affects the diffraction pattern?

No, there are other factors that can affect the diffraction pattern, such as the quality of the crystal and the wavelength of the incident radiation. However, the Bragg condition is a fundamental principle that must be satisfied for diffraction to occur.

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