Using an apparatus consisting of a double pulse ionization chamber, two amplifying channels, a coincidence circuit and a two-beam pulsed oscillograph, we measured the kinetic energy of each of the two fragments formed during nuclear fission. 780 cases of spontaneous U²³⁸ fission and about 4500 cases of U²³⁵ fission by slow neutrons were recorded. Using these data we plotted the statistical distributions of acts of spontaneous fission and fission with slow neutrons according to the energies of the two fragments. These distributions gave the following curves for the two fission methods: a) the energy spectrum of all fragments and that of light and heavy fragments separately; b) the distribution of acts according to the total kinetic energy of the two nuclear fragments; c) the distribution of fission fragments according to mass; d) the relation of the average total kinetic energy of the two fragments to the ratio of their masses; and e) the relation of the average kinetic energy of light and heavy fragments to their total kinetic energy. The results of the two methods of fission are quite similar. It was found that the total kinetic energy of the two fragments in spontaneous U²³⁸ fission was, on the average, 4 Mev less than the energy in U²³⁵ fission by slow neutrons.

Radioactive substances have a number of features which can be explained by the effect of selfirradiation. Systems containing radioactive elements are in a nonequilibrium state. The fraction of particles (molecules, atoms, ions) having increased energy exceeds the equilibrium value in these systems. The regions of the substance in which there is retardation of the ex- and ß-particles and the recoil atoms have a higher concentration than the equilibrium value of structure defects and increased free energy. These factors should affect the vapor pressure, solubility, dissociation pressure, equilibrium constants of chemical reactions, reactivity, specific heat, density, electrical conductivity, thermal conductivity and other properties of radioactive substances and also the character of their phase transformations. From this point of view a study is made of literature data on some properties of various radioactive substances.

Voids in the core of a nuclear reactor have an important effect on neutron leakage from the reactor. It is important that this effect be taken into account in computing the critical mass of the reactor. It is also frequently desirable to know the effect of empty channels on the neutron distribution outside the core.

In the present paper we consider the effect of a single hollow cylindrical channel on neutron diffusion. Expressions are obtained for neutron leakage through a channel located at the center of the reactor and for the additional neutron leakage (due to the existence of the channel) in the immediate vicinity of the channel. We also consider the effect of the neutron flux distribution along a channel on the applicability of the diffusion formulas.

The theoretical principles of the reduction of stable metallic oxides by calcium hydride are considered, on the basis of a study of the reduction reactions of zirconium and titanium oxides, Thermodynamical calculations and special experiments intended to clarify the mechanism of reactions between oxides and CaH₂ are used to compare the reducing activity of CaH₂ with those of the calcium and atomic hydrogen formed in its thermal dissociation. The view which exists in the literature, according to which the high reducing power of CaH₂ is explained by the action of the atomic hydrogen formed, is shown to be erroneous. It is shown that the principal reducing action in this process is effected by metallic calcium, formed by dissociation of CaH₂. Metallic calcium at temperatures of 1000° and higher reacts with chemically stable oxides not only in “the liquid but also in the vapor state, which creates favorable conditions for rapid and complete reduction reactions. It is also shown that the active hydrogen liberated when metals saturated with hydrogen are heated is capable, to some extent, of additionally reducing the oxides which contaminate these metals.