The Scattering of Slow Neutrons by Paramagnetic Crystals

The paramagnetic scattering of neutrons by anhydrous crystals of manganous fluoride, manganous oxide, and $\alpha$-ferric oxide was studied, using neutron transmission data obtained with the Columbia slow neutron velocity spectrometer. Details are given of the experimental arrangement, which permits measurements to be made with neutrons having wave-lengths up to 6.4A. The paramagnetic cross section, ${\sigma }_{\mathrm{pm}}$, may be separated from the total cross section in regions where there are no interfering crystal diffraction effects. Large values of ${\sigma }_{\mathrm{pm}}$ were found for the manganous compounds, but no paramagnetic scattering by $\alpha -{\mathrm{Fe}}_2{\mathrm{O}}_3$ was observed. The results are compared with the theoretical predictions of Halpern and Johnson. The dependence of ${\sigma }_{\mathrm{pm}}$ on the neutron wave-length was determined, and is compared with a theoretical form factor based on purely elastic scattering.