The chemical and magnetic structures of zinc ferrite and nickel ferrite have been investigated at room temperature by means of neutron diffraction. In agreement with previous x-ray investigations zinc ferrite has been found to possess a completely regular spinel structure with an oxygen parameter of 0.385±0.002. The diffraction peaks show no evidence of coherent magnetic scattering, whereas the background exhibits normal paramagnetic diffuse scattering. This eliminates the possibility of an antiferromagnetic structure at room temperature. In the case of nickel ferrite, calculated intensities based upon an inverted structure and the Néel model of ferrimagnetism are in good agreement with the observed intensities.

The saturation moment of ferromagnetic alloys has been considered from the point of view of the collective electron theory. Perturbations in band shape due to the fluctuating lattice potential are considered and are found to be more important in some cases than the simple effects of changing electron density characteristic of the usual treatment of alloys. The influence of order on the moment is treated on the basis of Slater's theory of the relation between the long range order and the energy bands in an alloy. Results of measurements of electronic specific heat and Hall effect are presented which make possible a model capable of explaining the unique effects of the order-disorder transformation in ${\mathrm{Ni}}_3$Mn on this basis. In other alloys, particularly those which do not follow the Slater-Pauling curve or the classical band model, the saturation properties are attributed to the perturbations in the band resulting from the presence in the lattice of ions with different potentials as seen by the itinerant electrons. The screening of the positive Coulombic charge on these ions is accomplished by fluctuations in local electron density of the Fermi gas in some cases and by localized bound states in other cases. The effect on the magnetic properties in these two alternative cases can be explained and correlated with changes in electrical resistivity on alloying. Atomic moments of the constituent atoms for some ordered alloys have been calculated and are in good agreement with the experimental values found by Shull in neutron diffraction experiments.

Neutron diffraction measurements are reported on a series of transition elements as an investigation into their magnetic structures. Scattering data have been taken for W, Mo, Nb, V, Cr, Mn, and Fe at various temperatures as low as 4.2°K, and these data are interpreted in terms of the magnetic structure existing in the pure metals. For the first four-named elements, no magnetic scattering either coherent or incoherent is found. Cr and $\alpha -\mathrm{M}\mathrm{n}$ are established as being antiferromagnetic with Néel temperatures of 475°K and 100°K, respectively. Paramagnetic scattering has been observed in manganese at room temperature, and the atomic moments determined for Cr and Mn follow the general trend of the Slater-Pauling curve. Magnetic superstructure effects and magnetic disorder scattering were looked for in iron and neither was found.

The general formula for the angular distribution in collisions between pairs of particles is simplified by performing explicitly all sums over magnetic quantum numbers. The resulting expressions involve coefficients introduced by Racah for the study of complex atomic spectra. The cross sections are expressed as series in Legendre polynomials, each coefficient in the series being manifestly real.

The general theory is then specialized for the case of nuclear reactions and scattering associated with one isolated resonance level of the compound nucleus. Formulas are derived for the various differential reaction cross sections and for scattering with and without change of channel spin. The interference terms between resonance and potential scattering are written explicitly, both for neutral and for charged particles.

A survey is given of the absorption of radiation in the energy range from 0.1 Mev to 6 Mev. Results of the theories of Compton effect, photoelectric effect, and pair production are given in the form of equations, tables, and curves. Necessary considerations in studying absorption coefficients are discussed and results of various workers are compared with theory. It is concluded that in this energy range the present theories give values of absorption coefficients which are in good agreement with those obtained experimentally.