The Slow Neutron Cross Section of H

The total neutron cross section of water has been measured with a slow neutron velocity spectrometer in the energy interval 0.003 to 100 ev. A treatment of the data for energies above 0.8 ev gave a value of 20.0 × ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ for the free neutron-proton cross section. Measurements of the total cross section of cyclohexane in the energy interval 0.8 to 100 ev were also made, and from these data a value of 20.1 × ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ was obtained for the free neutron-proton cross section. Measurements of the oxygen and carbon cross sections were made in order that the data on water and cyclohexane could be corrected to obtain the bound proton cross sections. The values obtained for these cross sections for the high energy neutrons are: for oxygen, 3.7 × ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$, and for carbon, 4.7 × ${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$. The data on water for energies below 0.8 ev yield evidence for the existence of a cross section for inelastic scattering of neutrons by water.