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I was looking up X-Ray crystallography using Bragg's Law:

$2d\sin\theta = n\lambda$

and I can understand the values of everything except this integer value $n$.

As far as my research got $n$ is used to describe the atom spacing in the crystal lattice, but I don't understand how you'd express $n$ or how it would describe it.

Could someone please explain this to me please?

Note: diagrams tend to be very useful in developing my understanding and if anyone has any reference to a video that might help as well. Thanks.

Do you actually do an experiment? I've used powder method and variable angle... –  Pygmalion May 17 '12 at 17:58
I think so, they did an x-ray crystallography experiment to find out the structure of the DNA molecule, so it would be the same with diamonds –  Olly Price May 18 '12 at 10:41

2 Answers 2

up vote 2 down vote accepted


I was wrong. The problem is as follows:

You can get several peaks for the same plane ($n=1$ peak, $n=2$ peak etc.). So if you, after measuring angles and making calculations, get plane distances $d$ and $\frac{d}{2}$, $\frac{d}{2}$ is just $n=2$ peak and $d$ is $n=1$ peak of the same set of diffraction planes.

Also, here is good explanation:


Oh okay, so it's more a case of finding out if the diffraction planes are larger or smaller than $\lambda$? Having done that, is there a way of finding out the distance between the diffraction planes precisely? –  Olly Price May 17 '12 at 17:12

Positive interference occurs when the waves reflected from two different "layers" differ by an (any!) integer number of wavelengths: $n$ is that integer.


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