Comment on "High energy neutron scattering from hydrogen using a direct geometry spectrometer"

The paper by Stock et al. [ Phys. Rev. B 81 024303 (2010)] reports measurements of neutron scattering from hydrogen in the 1–100 eV range of energy transfers, using the direct geometry MARI spectrometer at ISIS. Stock et al. claim that their measurements have comparable energy resolution to those on the inverse geometry VESUVIO spectrometer at ISIS. Most importantly, the main conclusions of Stock et al. with regard to VESUVIO are not valid unless this claim is true. Here we present overwhelming evidence that the energy resolution of the measurements in Phys. Rev. B 81 024303 (2010) is one to two orders of magnitude worse than on VESUVIO. It follows that the conclusion of Stock et al. that anomalous neutron cross sections measured on VESUVIO [ Chatzidimitriou-Dreismann et al. Phys. Rev. Lett. 79 2839 (1997)] are “the result of experimental issues using indirect geometry spectrometers” is unfounded.