Neutron Diffraction Studies of NaH and NaD

Neutron diffraction patterns for NaH and NaD are given from which it is established that the crystal structure is analogous to that of NaCl with the hydrogen centers replacing chlorine. It is shown that both sodium and deuterium scatter neutrons with a positive scattering amplitude whereas hydrogen scattering is characterized by a negative scattering amplitude. The coherent scattering cross sections for hydrogen and deuterium are determined as 2.0\ifmmode\pm\else\textpm\fi{}0.3 and 4.1\ifmmode\pm\else\textpm\fi{}1.2 barns, respectively. Using this value of the coherent scattering cross section for hydrogen and Melkonian's value of 20 barns for the total scattering cross section by a free proton, the scattering amplitudes characteristic of the two proton spin states have been evaluated, and these are in good agreement with the latest data on the scattering of neutrons by $o$- and $p$-hydrogen. The range of nuclear forces present in the neutron-proton triplet interaction is evaluated as 1.6\ifmmode\pm\else\textpm\fi{}0.2 \ifmmode\cdot\else\textperiodcentered\fi{} ${10}^{\ensuremath{-}13}$ cm.