# Measuring the phonon dispersion at edge of Brillouin Zone?

When it comes to measuring the phonon dispersion at the edge of a Brillouin zone, why are neutrons chosen and not photons?

• Photon dispersion or phonon dispersion? Jul 7, 2020 at 18:10
• Thanks, I corrected it.
– user248824
Jul 7, 2020 at 18:18
• Getting the required $k$ out of a photon is much harder. Jul 7, 2020 at 18:24

• Hi @ProfM. If we take X-ray photons (which have a range of their wave length from $10^{-11}$ to $10^{-8}$), then the wave vector isn't much smaller than the typical size of a BZ, is it? Also: Why do zone-center phonons have a smaller energy than zone-boundary phonons?