Neutron-scattering study of the impulse approximation in ZrH2

We report inelastic-neutron-scattering measurements of the neutron Compton profile, J(y) in polycrystalline ZrH2 over a range of momentum transfers between 35 and 109 Angstrom(-1). The measurements were performed using an inverse geometry spectrometer at a pulsed-spallation neutron source. The experimental results are compared with simulations calculated from st measurement of the density of starts of the hydrogen vibrations in ZrH2. Deviations from impulse approximation (IA) scattering and a form of the IA proposed by Stringari have been investigated. The deviations are manifest as both an asymmetry and a shift in centroid of J(y). Both effects become less significant as the momentum transfer is increased and the IA limit is approached. At high momentum transfers the symmetrization procedure of Sears successfully removes final-state effects from these data. We conclude that the neutron Compton scattering technique can provide accurate information about the behavior of tightly bound proton systems such as ZrH2.