Coherent Neutron-Proton Scattering by Liquid Mirror Reflection

A measurement of the coherent neutron-proton scattering amplitude, utilizing total reflection of slow neutrons from a liquid hydrocarbon, was first reported in 1950. As the result (-3.75±0.03×${10}^{-13\mathrm{}}$ cm) was significantly different from existing values, the measurements have been continued with a series of liquids in order to investigate systematic errors and to improve the accuracy. Final measurements have now been made utilizing a series of carefully purified hydrocarbon liquids, and a method in which no measurement of neutron wavelength is necessary. The ratio of the amplitude of hydrogen to that of carbon has been determined to 0.3 percent and the final value of the hydrogen amplitude, including the error (0.5 percent) in the carbon amplitude, is (-3.78±0.02)×${10}^{-13\mathrm{}}$ cm (standard error).