Measurements of the Neutron-Proton and Neutron-Carbon Total Cross Sections at Electron-Volt Energies

We have measured the neutron-proton total cross section in hydrogen gas and the neutron-carbon total cross section in pyrolytic graphite between 0.3-and 400-eV laboratory energy. After subtracting the capture cross section and molecular binding effects, we find 20.37±0.02 b for the free neutron-proton scattering cross section and 4.7534±0.0045 b for the free neutron-carbon cross section. The effects of these measurements and those of L. Koester on the singlet and triplet $n-p$ scattering lengths and effective ranges are discussed.