The index of neutron refraction of oxygen, nitrogen, helium, and argon has been studied by reflection of a neutron beam from a liquid gas interface and observation of decreasing reflectivity with increasing gas pressure. Results verify that the index for gases is given by the same formulas which hold for liquids and solids. Comparative measurements of the different gases then give values for the coherent bound scattering cross sections: assuming oxygen = 4.2 barns as a standard, nitrogen = 11 barns, helium = 1.1 barns, argon = 0.5 barn.

• Received 13 August 1951

DOI:https://doi.org/10.1103/PhysRev.84.969