Starting with the equation for the molecular structure factor F(S),

a) Show that the intensity of reflections along the (h 0 0) axis will be zero for all odd values of h when a two-fold screw axis is aligned along the crystallographic a-axis.

[Hint: Start by placing an atom at a specific set of x, y and z coordinates (in fractional cell unit cells), and generate its symmetry related atom in the unit cell]

b) Show that Friedels Law is Correct

For an atom with the atomic coordinates x= 1.51nm, y= 0.35nm, and z= 0.50nm in a tetragonal unit cell with lengths a= b = 20.nm, c= 30.0nm

a) Calculate the x, y, z coordinates in fractional unit cell lengths

b) If this is the only unique atom in the unit cell, calculate the phase angle  for the h= 2, k= 3, l= 4 reflection