Problem: Powder Diffraction of hcp and fcc Crystals

            Cobalt has two forms: -Co, with hcp structure (lattice spacing of a=2.51 Å) and -Co, with fcc structure (lattice spacing of Å). Assume that the hcp structure has an ideal c/a ratio. Calculate and compare the position of the first five X-ray powder diffraction peaks. The quantity can be used to characterize the peak positions (here is the wavelength of the X-ray radiation and is the scattering angle).