Scattering of Slow Neutrons by Ortho- and Parahydrogen

Abstract

Measurements have been made of the scattering cross sections of ortho- and parahydrogen for neutrons of energies in the range 10\ifmmode^\circ\else\textdegree\fi{}K to 30\ifmmode^\circ\else\textdegree\fi{}K. Using the Schwinger-Teller theory the results have been correlated with the scattering cross section of free protons for slow neutrons and with the range of a square-well $n\ensuremath{-}p$ potential. The measured cross sections show the energy dependence expected from the theory; they imply a free proton cross section of 19.7 barns and a force range of 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}13}$ cm, the first value agreeing within experimental error with the accepted figure, but the second falling significantly below the result 2.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}13}$ cm obtained by Breit, Thaxton and Eisenbud for the $p\ensuremath{-}p$ force. The singlet state of the deuteron is again shown to be virtual, and the possibility of a neutron spin of $\frac{3}{2}$ is eliminated since the data in this case would imply a free proton cross section of only 7 barns.