Understanding Bragg's Law in X-Ray Diffraction

Click For Summary
SUMMARY

The discussion centers on Bragg's Law in X-Ray Diffraction, specifically the equation nλ = 2d sin θ, which describes the condition for constructive interference of X-rays scattered by crystal planes. Participants question the assumption that reflected rays are parallel, noting that unlike Fraunhofer diffraction, X-ray diffraction does not utilize lenses or infinite distances. The consensus is that while the reflected rays are not perfectly parallel, the approximation holds due to the effective distance at which interference occurs, similar to the assumptions made in Fraunhofer diffraction.

PREREQUISITES
  • Understanding of Bragg's Law and its mathematical formulation
  • Familiarity with X-Ray Diffraction techniques such as rotating crystal and powder photography
  • Knowledge of wavefront behavior in electromagnetic waves
  • Concepts of interference and superposition in wave physics
NEXT STEPS
  • Research the derivation and applications of Bragg's Law in X-Ray Diffraction
  • Study the principles of Fraunhofer diffraction and its differences from X-Ray Diffraction
  • Explore the role of wavefronts in interference patterns in optics
  • Investigate the impact of crystal structure on X-Ray scattering and diffraction patterns
USEFUL FOR

Students and professionals in physics, materials science, and crystallography who are looking to deepen their understanding of X-Ray Diffraction and its underlying principles.

manofphysics
Messages
41
Reaction score
0
We all know, Bragg's law , n\lambda=2dsin\theta
where 2dsin\theta=path difference.
In the derivation of the path difference we take the two incident rays to be parallel which is perfect BUT we take reflected rays also to be parallel.How can this be since the reflected rays have to MEET for superposition to take place.
This is the same as in FRAUNHOFER diffraction, where we CAN take parallel rays due to the distance being effectively infinity or due to the use of LENS.
But we are not using a lens nor is the distance supposed to be very large(infinity) in the experimental methods of Xray diffraction ( rotating crystal, powder photograph etc.).
So, how is it that this formula works?
 

Attachments

  • bragglaw.gif
    bragglaw.gif
    6.7 KB · Views: 602
Physics news on Phys.org
I'm missing something here.

You have parallel incident waves reflecting from parallel planes...why wouldn't the reflected rays also be parallel?

Or are you trying to treat the wavefront as a single point rather than a plane?
 
Last edited:
when an EM wave strikes an atom, a spherical wave front is emitted. ie waves are emitted in ALL directions . Now we are considering the emitted rays by two atoms which are parallel,
But the parallel rays will not meet for interference, we need to use a lens...
(I am using an analogy of diffraction in optics here. as both are almost similar, I think)
 
The rays do meet because the rays are not exactly parallel. They are only approximately parallel. And the approxmation is good enough because the place where they meet is "far" away.
 
So, I guess it is the same assumption that we take in Fraunhofer diffraction.
Thanks for the reply ,Edgardo.
 

Similar threads

Undergrad Understanding Ewald's sphere in the context of X-Ray diffraction
  • · Replies 3 ·
Replies
3
Views
6K
Undergrad Why the reflected angle is the same as incident in x-ray diffraction?
  • · Replies 4 ·
Replies
4
Views
5K
Undergrad Why X-ray scattering in crystalline solids is elastic?
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad What happens to X-rays if they do not meet Bragg's law?
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad Van Laue Formulation: X-ray Diffraction from Crystal Structure
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Is There an Analogous Law for X-ray Diffraction Minima?
  • · Replies 2 ·
Replies
2
Views
3K
Graduate What Are the Key Insights on Bragg/von Lau Scattering in X-Ray Experiments?
  • · Replies 2 ·
Replies
2
Views
3K
Undergrad High Resolution X-Ray Diffraction: Explained
  • · Replies 2 ·
Replies
2
Views
5K
Undergrad What explains the sharpness of XRD peaks?
  • · Replies 4 ·
Replies
4
Views
4K
Undergrad Questions About Bragg's Law of X-Ray Diffraction
  • · Replies 54 ·
2
Replies
54
Views
10K