Cross Section of Slow Neutrons on Parahydrogen

The total cross section for interaction of slow neutrons by parahydrogen has been measured to 0.1%. A pressure dependence has been found whose origin is obscure. By extrapolation to $p=0$, a value for the coherent scattering length of (-3.707\ifmmode\pm\else\textpm\fi{}0.008) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}13}$ cm is found, in agreement with the liquid-mirror result of (-3.721\ifmmode\pm\else\textpm\fi{}0.004) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}13}$ cm.