Neutron-Proton and Neutron-Carbon Scattering Amplitudes

Measurements of the $n-p$ and $n-\mathrm{C}$ coherent atomic scattering amplitudes are described. The results $a_{\mathrm{H}}=-3.740\mathrm{}\pm 0.003$ fm and $a_C=6.648\mathrm{}\pm 0.003$ fm were obtained by reflection measurements on seventeen various liquid mirrors with the neutron gravity refractometer, for which a more accurate method of evaluation is given. The mirrors were composed of the elements hydrogen, carbon, and chlorine. The atomic scattering amplitude of chlorine was found to be $a_{\mathrm{Cl}}=9.580\mathrm{}\pm 0.002$ fm. The new $a_{\mathrm{H}}$ is of importance for describing the $n-p$ system.