Question

Is the peak density (number of peaks per 2θ angle) higher at low 2θ or at
high 2θ in X-ray diffraction spectra? Why? Use a cubic crystal as an example
to interpret this phenomenon.

Answer 1

If you meant the number of peaks at a given 2theta interval, in principle, it will be more at high angles. If you imagine the Ewald construction and reciprocal lattice, you can see that low angle shells have less radius and therefore less number of reflections corresponding to it.

If you meant the number of peaks appearing at the same angle (it's called multiplicity), then it depends upon the symmetry of the crystal system. It's more appropriate to use the term X-ray diffractogram or X-ray diffraction pattern. "Spectra" can be misleading (although one can argue otherwise).