  Liquid deuterium is a fluid between the quantum and classical regimes. It
attracts interest from fundamental research for the verification of quantum
calculations but also from neutron physics as it is a widely used neutron
moderator medium. We have measured the scattering cross sections of liquid
ortho-deuterium in the ultracold-neutron range for four different temperatures
(19-23 K) and compared them with calculations from a parameter-free analytical
calculation model as well as with previous measurements at 19 K by another
research group. All three show remarkable agreement, which establishes the
validity of the calculation model and proves it is a reliable basis for the
derivation of scattering kernels. The deconvolution of our measured
transmission data changed the cross section results noticeably only for
neutrons faster than 10 m/s. We found the total scattering cross section of
liquid deuterium to be inversely proportional to velocity, as is predicted by
theory.
