Hi, I have yet another problem with this diffraction thing. I have little clue on these questions: e) The radius of the O^2- ion is assumed to be 0.126 nm. By x-ray diffraction experiments the dimensions of the unit cells for MgO, CaO, SrO and BaO has been determined to be 0.4213 nm, 0.4811 nm, 0.5160 nm and 0.5539 nm. All four compounds has the NaCl structure. Calculate the radii of the cations: Mg^2+, Ca^2+, Sr^2+ and Ba^2+. f) ZnSe has a cubic close packed structure of the anions, but with the cations in the tetrahedral holes. How large a fraction of the tetrahedral holes are occupied in this structure? Any hints?