The Diffraction of Neutrons by Crystalline Powders

The powdered crystal technique, which has been shown for the case of x-rays to be best suited for accurate, integrated intensity measurements, has been applied to neutron diffraction. Neutrons from the Clinton pile are monochromatized by reflection from a single crystal and the diffraction patterns produced when these neutrons fall on specimens of crystalline powders have been studied. These studies have given (a) a check on some aspects of the diffraction theory, (b) the magnitude and sign of the scattering amplitudes from various nuclear species from which information is obtained on the spin dependence of the scattering, which has a bearing on the magnitude and range of nuclear forces, and (c) an improvement in the techniques and a better understanding of the problems involved so that results can be more readily obtained on the diffraction by other crystals, such as those containing hydrogen or deuterium.

Diffraction measurements have been obtained on diamond, graphite, Al, Na, NaBr, NaCl, and NaF in which all intensity measurements were standardized against diamond to which a definite cross section was assigned on the basis of total cross-section measurements. The scattering of carbon, Al, and F was found to have no measurable spin dependence. The scattering by Na, however, shows a considerable spin dependence as evidenced by a Bragg scattering cross section of 1.51 barns as against a total scattering cross section of 3.7 barns. Measurements have been made on a number of other crystals with the purpose of determining the phase of scattering. A table showing the scattering phase for a number of elements is given.