X-ray diffraction; atomic form factor

[physics_fun]

Hey,

I'm working on a problem about the atomic form factor. I found that the atomic form factor of an fcc lattice of Buckyballs (C60 atoms) looks like f~(sin(Gr))/G multiplied bij some constants.

The question is now to explain from this atomic form factor why the (2,0,0) X-ray diffraction peak is much weaker (compared, for example, to the (1,1,1) peak).

I tried to put the numbers in, but every time I try this, I get (almost) the same answers for the two peaks...:(

What am I doing wrong?

edit: r=constant

 

[espen123]

that is because, 002 is at an higher 2theta value, if you look at braggs law you can see that the d spacing is invers related to theta. Bigger miller index, means smalle d-spacing which in turns meens a larger theta value. And as the form factor falls of with bigger theta values, that is the explanation..

 

[avisha03]

Hey!
Can u explain how did you calculate the form factor?
I don't know how to pass from the vectoric experession to an expression I'll be able to calculate..
tnx a lot!