NEUTRON-SCATTERING STUDY OF THE IMPULSE APPROXIMATION IN ZRH2

We report inelastic-neutron-scattering measurements of the neutron Com pton profile, J(y) in polycrystalline ZrH2 over a range of momentum tr ansfers between 35 and 109 Angstrom(-1). The measurements were perform ed using an inverse geometry spectrometer at a pulsed-spallation neutr on source. The experimental results are compared with simulations calc ulated from st measurement of the density of starts of the hydrogen vi brations in ZrH2. Deviations from impulse approximation (IA) scatterin g and a form of the IA proposed by Stringari have been investigated. T he deviations are manifest as both an asymmetry and a shift in centroi d of J(y). Both effects become less significant as the momentum transf er is increased and the IA limit is approached. At high momentum trans fers the symmetrization procedure of Sears successfully removes final- state effects from these data. We conclude that the neutron Compton sc attering technique can provide accurate information about the behavior of tightly bound proton systems such as ZrH2.