High-energy neutron scattering from hydrogen using a direct geometry spectrometer

Abstract

Deep inelastic neutron scattering experiments using indirect time-of-flight spectrometers have reported a smaller cross section for the hydrogen atom than expected from conventional scattering theory. Typically, at large momentum transfers, a deficit of 20-40% in the neutron scattering intensity has been measured and several theories have been developed to explain these results. We present a different approach to this problem by investigating the hydrogen cross section in polyethylene using the direct geometry time-of-flight spectrometer MARI with the incident energy fixed at a series of values ranging from Ei=0.5 eV to 100 eV. These measurements span a much broader range in momentum than previous studies and with varying energy resolutions. We observe no momentum dependence to the cross section with an error of 4% and through a comparison with the scattering from metal foil standards measure the absolute bound cross section of the hydrogen atom to be σ(H)= 80 ± 4 barns. These results are in agreement with conventional scattering theory but contrast with theories invoking quantum entanglement and neutron experiments supporting them. Our results also illustrate a unique use of direct geometry chopper instruments at high incident energies and demonstrate their capability for conducting high-energy spectroscopy.

Comment on “High-energy neutron scattering from hydrogen using a direct geometry spectrometer”

“…In reality, the energy resolution of VESUVIO is between one and three orders of magnitude better than that of the measurements in reference [1]. This implies that the measurements in ref [1] provide no basis for the claim of Stock et al that anomalous neutron cross sections measured on VESUVIO [2] are "the result of experimental issues using indirect geometry spectrometers".…”

“…This implies that the measurements in ref [1] provide no basis for the claim of Stock et al that anomalous neutron cross sections measured on VESUVIO [2] are "the result of experimental issues using indirect geometry spectrometers".…”

“…The full width at half maximum (FWHM) of lead peaks on VESUVIO is ~0.25 eV compared with between 4 and 55 eV on MARI. [1]. After taking into account the slight broadening due to the momentum distribution of the lead atoms, the energy resolution function on VESUVIO has a FWHM of ~0.2 eV [5] compared with between 4 and 55 eV on MARI.…”

“…Such measurements are a welcome development. Unfortunately ref [1] may mislead readers who are less familiar with the technical details of neutron spectroscopy. Stock et al claim that their hydrogen measurements on the MARI direct geometry spectrometer at ISIS, have comparable energy resolution to measurements on the VESUVIO inverse geometry spectrometer at ISIS.…”

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AbstractThe paper in the title [1] reports measurements of neutron scattering from hydrogen in the 1-100 eV range of energy transfers, using the direct geometry MARI spectrometer at ISIS. 2

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