# Vector Diagrams of Structure Factors

### Vector representation of F in complex plane

### Friedel's law

Note that f^{o} and the real part of the
anomalous scattering (f ') are colinear, and that f " is 90 degrees phase shifted.
Show that the crucial point is the mixing of cos and sin terms and that the little blue
arrow to the left does NOT represent a cos term as in normal cases but a sin term ! Hint :
f = ( f^{o}+f '+ if ") � (cos(phi) + i sin(phi))

Note that both magnitude of F (and thus, intensity) *and*
phase of F are different for F and -F. Fp = structure factor of protein alone, Fa is real
part (both f' and fo) of anomalous scatterer, Fa" is f".

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Last revised
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