Vol 10, No 4 (2016)

A unique cold moderator based on a mixture of mesitylene and m-xylene is developed for the IBR-2 pulsed reactor. If combined with a standard warm-water moderator, it provides a high neutron flux in a wide wavelength range. The advantages of the use of this composite moderator in neutron-diffraction texture analysis are discussed using the example of a sample of slate (formed from five minerals) studied using the SKAT diffractometer. The diffraction data obtained in experiments with warm-water and composite moderators are compared.

The formation of radiation defects in Si under 1–10-MeV proton bombardment is analyzed. Numerical simulation is carried out, and histograms of the distribution of the energy transferred to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. Single Frenkel pairs with closely located components are produced in the first range (small energies). Recoil atoms of the second range have an energy sufficient for the production of a displacement cascade. As a result, nanoscale regions with high densities of vacancies and different types of their complexes appear. In addition, as the energy of the primary knocked-out atoms increases, the average distance between genetically related Frenkel pairs increases, and, as a consequence, the fraction of pairs that are not recombined under bombardment increases.

Techniques for measuring the residual stresses in bilayer thermal barrier coatings of a NiCrAlY alloy metal sublayer and 8-wt% stabilized ZrO₂–8Y₂O₃ ceramic upper layer are developed with the inhomogeneous composition and stress relaxation upon removal of the top layers taken into account. The outer ceramic layer is shown to undergo quenching-induced tensile stress up to 200 MPa, whereas the metal sublayer is subjected to compressive stress of 600 MPa which is associated with an increase in the specific volume as a result of the formation of a thermally grown oxide (TGO).

The results of studying the effect of the electron–ion plasma treatment of the surface of tool hard alloys in plasma-forming gases at varying ionization energy and varying atomic weight on the structural phase state and abrasive-wear and metal-cutting resistance of the surface layer are described.

A technique for the deposition of composite coatings based on Ti–Al intermetallic compounds by vacuum-arc plasma discharge is developed. X-ray diffraction data on the obtained coatings are reported. The effect of deposition modes on the intermetallic-compound contents in the coatings is established.

The process of GaSe surface oxidation is investigated. The work function is revealed to vary by 0.5 eV within a few hours after the formation of a cleaved facet of the semiconductor surface. It is demonstrated that low-energy laser irradiation with a wavelength of 650 nm leads to the generation of an intrinsic oxide on the crystallite surfaces. On account of continuous exposure to laser radiation for 6 h, the work function of the GaSe surface increases by 1 eV, i.e., becomes twice as large as that obtained without irradiation.

The results of experimental and theoretical investigations of the X-ray diffraction patterns from double- or triple-crystal systems and a thick absorbing crystal are presented. The period of the fringe patterns from the double-crystal system is calculated. An expression for calculating the linear enlargement factor in the presence of a crystal-magnifier is deduced. It is proved that the crystal-magnifier does not change the interference pattern but only increases its angular sizes in the scattering plane.

An image of the entrance of high-energy ions of krypton, xenon, and bismuth on the surface of polyethylene terephthalate (PET) and mica is obtained. It is shown that in both cases the tracks have the appearance of protuberances. The formation of protuberances is associated with the destruction of material in the region of the track, the formation of amorphous structure, and the removal of low-molecular-weight radiolysis products as gaseous substances. Storage of the irradiated PET samples in water and a weak alkaline solution for several hours changes the surface topography due to hydrolysis of the material and the removal of radiolysis products into the solution. The kinetics of etching tracks in a weak alkaline solution and the formation of pores are studied. The stream function, electrical resistance, and permeability of the tracks in KCl, LiCl, MgCl₂, and BaCl₂ electrolytes are measured. The surface charge of the tracks is calculated from these values.

The energy dependence of the electron inelastic mean free path, λ(E), in silicon oxide and silicon nitride is experimentally determined via Auger electron spectroscopy according to Auger signal attenuation with varying film thickness. Silicon-oxide- and silicon-nitride films are formed on different metal substrates by means of plasma-enhanced chemical vapor deposition. Analysis of the results and their comparison with theoretical data indicate that, in the chosen material, variations in the electron mean free path versus their energy are estimated more reliably by means of experiments than through the use of universal theoretical curves. It appears that the results obtained in this work can help in the more accurate determination of the width and location of interfaces in multilayer structures.

The helicoidal magnetic structure of a MnGe compound doped with 25% Fe is studied by means of small-angle neutron scattering in a wide temperature range of 10–300 K. Analysis of the scattering-function profile demonstrates that magnetic structures inherent to both pure MnGe and its doped compounds are unstable. The doping of manganese monogermanide is revealed to lead to higher destabilization of the magnetic system. In passing from MnGe to Mn_0.75Fe_0.25Ge, the magnetic-ordering temperature T_N decreases from 130 to 95 K, respectively. It is demonstrated that, at temperatures close to 0 K, the intensity of the contribution to scattering from stable spin helices decreases and the intensity of scattering by spin helix fluctuations increases with increasing impurity-metal concentration. An increased intensity of anomalous scattering caused by spin excitations existing in the system is observed. Helicoidal fluctuations and spin excitations corresponding to low temperatures indicate the quantum nature of the instability in the doped compound. However, MnGe doping with Fe atoms has no influence on the compound’s magnetic properties at temperatures of higher than T_N. The temperature range of short-range ferromagnetic correlations is independent of concentrations and is restricted by temperatures T ranging from 175 to 300 K.

New optimization criteria for a class of instruments, neutron reflectometers, are established by analysis of the reflectivity measurements. Luminosity of the reflectometer is defined as the neutron flux incident onto the sample surface on conditions that the measurement is made with a given momentum transfer resolution. The correct choice of the working wavelength and realization of measurements with optimum parameters of the neutron beam increase luminosity in several times. Standard schemes for the reflectivity measurements with monochromatic and white beams are considered. Optimization of the reflectivity measurements generally requires numerical calculations. Analytically, its potential is demonstrated by considering thermalized neutron beams. Such innovations as neutron-optical velocity selector, small-angle Soller collimators with traps for neutrons reflected from the channel walls and neutron fan beam time-of-flight technique are proposed to further increase the luminosity of reflectometers.

Density functional methods involving the B3LYP functional and M062X, WB97XD, and B97D ones optimized for calculations of long-range interactions are used to carry out theoretical analysis of the structural and thermodynamic parameters of complementary adenine-thymine, adenine-uracil, and guanine-cytosine base pairs with hydrogen bonds. The calculated values of the structural and thermodynamic parameters are corrected according to the basis superposition error. The enthalpy factor is demonstrated to prevail over the entropy one during the formation of the guanine—cytosine complex, indicating that the equilibrium constant is of great importance. It is discussed whether the M062X, WB97XD, and B97D functionals can be applied to describe hydrogen-bonded systems.

The emission angle and the transverse momentum distributions of projectile fragments (PFs) produced in fragmentation of ²⁸Si on C and CH₂ targets at 775 A. MeV are measured. It is found that the mean emission angle and the mean transverse momentum increase with the decrease of the charge of PFs for the same target, and no obvious dependence of angular and transverse momentum distribution on the mass of target nucleus are found for the same PF. The cumulative squared transverse momentum distribution of PF can be well explained by a single Rayleigh distribution. The temperature of PF emission source do not depend on the size of PF and mass of target for PF with charge 5 ≤ Z < 13.

The results of experimental investigation of the combined action of 500-keV protons and ~20-eV oxygen plasma on thin polyimide films are presented. The samples are irradiated with a proton fluence of 10¹⁴–10¹⁶ cm^–2 and an oxygen plasma fluence of ~10²⁰ cm^–2. The transmission and Raman spectra of the films, which are measured at different stages of sample irradiation, are compared. Data on the mass loss of the samples as a result of surface erosion are presented.

A dynamic theory of the coherent X-ray radiation of a divergent beam of relativistic electrons crossing a single-crystal plate in the Bragg scattering geometry is developed. The angular densities of parametric X-ray radiation and diffracted transition radiation of a beam of relativistic electrons are calculated numerically via averaging over the angular distribution of relativistic electrons in the beam in the form of a two-dimensional Gaussian distribution. It is shown that the influence of the divergence of a high-energy electron beam on the angular density of diffracted transition radiation is significantly greater than on that of parametric X-ray radiation.

Bulk carbon nanomaterials are synthesized using low-temperature plasma generated by a direct current plasma torch upon the pyrolysis of soot in the presence of catalysts and hydrocarbon gases. Data on the influence of the synthesis parameters and substrate material on the phase composition and morphology of the nanostructures are obtained and discussed using scanning electron microscopy and X-ray diffraction and thermal analysis.

The interaction between Li–D films obtained via deposition in magnetron discharge with nitrogen and oxygen is investigated. It is shown that exposure to these gases at a pressure of 4000 Pa does not lead to a significant decrease in the amount of deuterium in the film unlike the case of water vapor. The release of deuterium from Li–D films during thermal-desorption analysis occurs mainly in a narrow temperature range at 650–700 K in the case of as-deposited films and after gas exposure. The amplitude of the low-temperature region in the TDS spectrum increases after oxygen exposure.

Features of the temperature dependence of the conductivity of nanoisland metal films are investigated. It is established that the conductivity is affected, aside from via thermal activation, by ion-field processes caused by the surface diffusion of atoms. The variation in the ion-field conductivity is shown to have an activation character.

The coexistence of the amorphous structure and crystalline hexagonal structure of ice near its melting point at normal pressure is confirmed by comparing the diffraction patterns of diffuse X-ray scattering for different amorphous structures. The diffuse X-ray scattering at an ice sample maintained at a temperature of–10°C is continuously recorded for a long time. Continual variations in the nature of diffuse scattering until its complete disappearance are revealed. The disappearance of diffuse scattering indicates the metastability of amorphous ice near its melting point with a lifetime of about 15 days.