Inelasticity Effect on Neutron Scattering Intensities of the Null-H 2 O

Abstract

Time-of-flight (TOF) neutron scattering measurements have been carried out for liquid null-H₂O, in which the average coherent scattering length of hydrogen atoms is zero. In order to determine the inelasticity effect depending on both the scattering angle and the neutron flight path ratio, γ[=l_s/(l₀+l_s), l₀ and l_s denote the moderator-sample and sample-detector distances, respectively], neutron scattering measurements have been performed using three neutron spectrometers, HIT-II, RAT, and SWAN, installed at KENS, Tsukuba, Japan. The self-scattering intensity for the null-H₂O was derived by subtracting the known O–O partial structure factor from the observed scattering cross-section. It has been revealed that the magnitude of the inelasticity distortion involved in the self-scattering term is still significant even at a smaller scattering angle than that expected from the first-order inelasticity correction formulas proposed in the literature. The inelasticity distortion in the self-scattering term is found to be preferably reduced by applying the small flight path ratio. An empirical but useful correction procedure for the inelasticity effect is developed using the self-scattering intensities observed for the null-H₂O. The present correction procedure is applied to the scattering cross-section observed for aqueous 3 mol% alanine solution which involves 20% H of exchangeable hydrogen atoms, and to the first-order difference function Δ_H(Q) observed for 4 mol% lithium benzoate heavy water solutions in which H/D isotopic substitution has been applied for benzyl-hydrogen atoms within the benzoate ion. The results indicate that the present inelasticity correction procedure works satisfactorily for the scattering intensity from the aqueous solution containing H atoms.