X-ray Diffraction: Why Are Peaks of Different Intensities?

[abcdmichelle]

This is not really a homework question but a more general plea for an explenation from someone! :)

In x-ray diffraction, you get a graph with different peaks that are particular to the composition of your sample. But, why are some peaks are of higher intesities then others? What is it about the sample/crystal structure that makes some peaks greater then other at certain angles?

thank you!

 

[nickjer]

The intensity falls off with an increasing angle of diffraction (corresponding to larger Miller indices) due to the angular dependence in the atomic form factor. That is why the peak for (110) in bcc is the largest. It is briefly discussed on Wikipedia on the "Structure factor" page, but you can also find it discussed in books.

Also, if the mineral is not monotonic (more than one element), then different elements can have different form factors leading to varying intensities.