Interference Phenomena of Slow Neutrons

Abstract

Various experiments involving interference of slow neutrons have been performed in order to determine the phase of the scattered neutron wave with respect to the primary neutron wave. Theoretically this phase change is very close to either 0° or 180°. The experiments show that with few exceptions the latter is the case. The evidence is based on the following types of measurements: (a) measurement of the intensities of Bragg reflection of various orders of many crystals, and comparison with the theoretical values of the form factor; (b) total scattering cross section of gas molecules for wave-lengths long compared with the molecular dimensions; and (c) determination of the limiting angles for total reflection of neutrons on various mirrors. The elements Ba, Be, C, Ca, Cu, F, Fe, Mg, N, Ni, O, Pb, S, and Zn were found to scatter neutrons with 180° phase difference; Li and probably Mn scatter with zero phase difference. The five elements I, Br, Cl, K, and Na behave alike and the phase with which they scatter is tentatively identified as 180°. Coherent scattering cross sections have been determined for several elements.