East European Journal of Physics

4-24

Authors: S.V. Lytovchenko

The overview presents a historic retrospective and current state of research of structure, properties and application of hightemperature silicide materials in science and engineering. These materials, particularly construction and functional materials based on or involving silicide refractory metals, are a most important alternative class of materials which adequately complete with special alloys, intermetallic metals, and ceramics that are traditionally used at high (above 15000C) temperatures in oxidizing and other aggressive environments. The paper analyzes the data available on constitutional diagrams, particularly on molybdenum-silicon and tungsten-silicon systems. Also, it shows differences in descriptions of diagrams given by different authors and considers some crystallochemical and physical properties of some high-temperature silicides. The paper reviews areas of application of high-temperature silicide materials of various types (layered and multiple-phase composites, consolidated powders, film structure, three-dimensional materials), and presents details of the challenges encountered in the process of creation and application of high-temperature protecting silicide coatings, as well as possible ways to improve their performance. It is noted that lack of unified approach to presentation and correlation of research results as well as to description of real performance of materials is a substantial problem in creating new high-temperature silicide materials.

35-46

Authors: Yu.M. Poluektov

Self-consistent approach for interacting phonons description in lattice, which generalizes Debye model, is proposed. Notion of “selfconsistent” phonons is introduced, speed of which depends on temperature and is determined from non-linear equation. Debye energy is also a function of temperature in this approach. Thermodynamics of “self- consistent” phonon gas is constructed. It is shown, that at low temperatures there is a correction propotional to the seventh power of temperature to the cubic law of specific heat dependence on temperature. This may be one of the reasons why cubic law for specific heat is observed only at rather low temperatures. At high temperatures the theory predicts linear deviation from Dulong-Petit law, which is observed experimentally.

64-72

Authors: V.I. Kasilov, S.P. Gokov, A.N. Dovbnya, S.A. Kalenik, K.S. Kokhnyuk, S.S. Kochetov, A.A. Khomich, O.A. Shopen

In this paper, to obtain streams of thermal and epithermal neutrons are used delayed neutrons emitted from the target with a fissile material. The target preliminarily activated with help of electron beam from linear accelerator with an energy of 20 MeV and a power of 9 Watts. At the same time to obtain a stream of thermal as well as epithermal neutron density 6 10-5 n / (cm 2 s) The results of experiment are presented where half-decay curves have been measured of emitting delayed neutrons radioactive nuclei produced in the fission process. It has been shown that the activated target, which contains the fissile material, presents a compact small size source of delayed neutrons. It can be delivered to the formator where thermal and epithermal neutrons are formed during a certain time period with help of the moderator, absorber and collimator. Then this target is moved to the activator being replaced with another target. Thus, pulsed neutron flux is produced. The duration of neutron pulse corresponds to the presence time of the activated target in the formator, and time interval between pulses is determined by the delivery time of the target from the activator to the formator. Given that the yield of neutrons from the target is directly proportional to the power of the beam of accelerated electrons, shows that the beam power of 1.5 - 3 kW, the flux density of thermal and epithermal neutrons can reach the values of (2-3) 109 n / (cm2 s). Such a neutron beam can be used in nuclear medicine, in particular, in neutron capture therapy of oncologic diseases.

84-87

Authors: D.G. Malykhin

A calculation of X-ray diffraction on the dislocation structure of polycrystalline materials with the biaxial anisotropy of the crystal lattice has been carried out. The task was reduced to definition of the field of lattice distortion in this neighborhood applied to edge dislocations of the «c» type in condition of anisotropy of elastic modules of a crystal. As a result of general solution of this task, a parameter of spatial anisotropy of the distortion field was defined from elastic modules and further included into tensors of transformation of both initial isotropic model of this field and its coordinates. According to this principle a modified mathematical model of the field of elastic atomic displacements in the neighborhood of an edge dislocation has been built. The final result shows that this anisotropy entirely reflects onto dislocation specific parameters of distortion that can be obtained by an XRD method for determination dislocation distributions and density. It is noted that for hcp metals widely used, accounting of this anisotropy would be reduced to small corrections of parameters.

92-100

Authors: G.G. Lesnyakov, A.N. Shapoval

also, the electron beam injection in the additional toroidal magnetic field (16 coils, making up 60% to 76% of the total toroidal field). In the stationary toroidal magnetic field, the turns of the electron beam have been visualized by scanning the poloidal vacuum chamber cross-section with a luminescent rod. The measurements have made it possible to determine a decrease in the ratio of stray environment vertical magnetic fields to toroidal-coil magnetic field down to z/BT ≈ 1×10-3 at magnetic fields ВТ = 0.0225 - 0.15 T, and also, to estimate the prospect of the ratio decrease to z/BT ≈ 1×10-4 as the toroidal magnetic field increases up to ВТ ≥ 0.45 Т.