Coherent- and Incoherent-Scattering Laws of Liquid Argon

Abstract

The inelastic-scattering functions for liquid argon have been measured at 85.2 K. The coherent-scattering function was obtained from a measurement on pure ${\mathrm{A}}^{36}$ and the incoherent-scattering function was derived from the result obtained from the ${\mathrm{A}}^{36}$ sample and the result obtained from a mixture of ${\mathrm{A}}^{36}$ and ${\mathrm{A}}^{40}$ for which the scattering is predominantly incoherent. The data, which are presented as smooth scattering functions at constant values of the wave-vector transfer in the range 1.0-4.4 ${\mathrm{\AA{}}}^{\ensuremath{-}1}$, are corrected for multiple-scattering contributions and for resolution effects. Such corrections are shown to be essential in the derivation of reliable scattering functions from neutron-scattering data. The incoherent-scattering function is compared to recent molecular-dynamics results and the mean-square displacement as a function of time is derived. The coherent-scattering function is compared to molecular-dynamics results and also, briefly, to some recent theoretical models.