No 8 (2024)

A linear position-sensitive neutron detector based on two silicon photomultiplier and an organic light guide has been developed. Determination of the coordinate of the neutron hitting the detector comes from analyzing the amplitude of the signal received from two silicon photomultipliers located at the ends of the light guide. The results of measurements using a collimated ²⁵²Cf source and two types of detectors based on silicon photomultipliers from SensL with a diffusion reflector and from Hamamatsu without and with a diffusion reflector are presented. Signals from silicon photomultipliers are recorded using an analog-to-digital converter. The neutron impact coordinates were analyzed using the amplitude characteristics of the photosignal. For a detector based on silicon photomultiplier from SensL, there was no obvious dependence of the signal amplitude on the coordinate of the neutron detection event, in contrast to detectors from Hamamatsu. The resolution of the detector coated with a diffusion reflector was about 10 mm, and without the diffusion reflector it was approximately 5 mm.

Neutron scintillation detectors based on ZnS(Ag)/LiF, solid-state photomultipliers, and an organic glass lightguide developed at INR RAS are successfully used in neutron diffractometers facilities at INR RAS as a replacement for standard counters based on ³He. These detectors use optical lightguide with diffuse reflection, which makes it possible to multiply the recorded signal (up to 95 photoelectrons) in comparison with detectors with wavelength shifting fibers. The paper describes 2 types of types of bias circuit for silicon photomultipliers. A method of dynamic bias has been proposed, which makes it possible to reduce the recovery time of a silicon photomultiplier and 8 times increase the loading capacity of neutron detectors. Simulation and comparison of 2 types of preamplifiers showed an increase in the loading capacity. The new electronics makes it possible to increase the loading capacity of the detectors up to 400 kHz. A circuit for digital control of discrimination thresholds has been developed and described. A new data acquisition system for time-of-flight neutron diffractometers for 80 detectors with the possibility of scaling has also been developed.

Multiwire position-sensitive neutron detector with two layers of boron-10 was developed to detect both thermal and fast neutrons. Sensitive dimensions of two coordinate neutron detector are 50 × 50 mm. New detector characteristics are compared with ones of 100 × 100 mm detector built earlier which we used in neutron flux spatial distribution measurement. Plane-parallel design of new detector has symmetrical structure with respect to wire anode and also includes two intermediate grids and two cathodes made of parallel wires with 2 mm pitch and two silicon substrates coated boron-10 layers of 0.003 mm thickness. Detector geometry, working gas mixture and pressure are chosen so as to ensure full absorption of secondary alpha particle from reaction with thermal neutron within detector gas medium half thickness. Neutron coordinates are determined from measured ionization loss pulse heights produced by secondary nucleus. Detector expected efficiency to thermal neutrons is about 5%. The detector can be used in small-angle and diffraction scattering setups in condensed matter physics.

Using the methods of X-ray diffraction analysis, X-ray spectroscopy and theoretical physics, we studied the patterns of changes in the atomic, electronic and magnetic subsystems in ferrites of variable composition Mn_xZn_yFe_zO₄ associated with the formation of clusters differing in the composition of cations. Experimentally detected clusters, which appear in X-ray diffraction patterns as a halo, are characterized by a certain superposition of ion states, the magnetic moment of which depends not only on the spin of the electron, but also on its orbital moment and the spin of the nucleus. A phase transition was discovered in the mesoscopic cluster structure from manganese-containing clusters, caused by the interaction of trivalent manganese ions with oxygen ions, to clusters with a predominance of di- and trivalent manganese ions with oxygen ions. It is found that the clustered structure of manganese-zinc ferrites is responsible for the appearance of extreme magnetic properties; the maximum corresponds to a change in the dominant type of clusters. It is found that with an increase in mass density, a repopulation of energy states occurs as a decrease in the states of the low-energy electron group and an increase in the high-energy Fermi surface in the form of a saddle. It has been established that the peculiarities of condensation of the fundamental and soft modes of complexes (clusters) containing manganese and oxygen ions lead to changes in the physical parameters of the samples.

Basing on the data of small-angle neutron scattering for the nanocomposite composed of fullerene C₆₀ (16.5 wt. %) in the matrix of isotactic polypropylene, we received information on clusterization of nanoparticles and defined their geometric parameters and dimensionality. In this paper, we propose interpretation of particle aggregation possessing the properties of surface fractal in the size range up to 80 nm observed using small-angle neutron scattering method. Basing on the well-known theories of defect structures of a fullerene molecule C₆₀ in non-Euclidean metrics, in particular, of disclinations and monopole in two-dimensional spherical Gödel space—time, we formulate a lattice version for the action of monopole gas, in which with the lattice Monte Carlo method, using abelian projection, we estimate the energy of monopole currents at different monopole concentrations. In frames of the proposed model, it is possible to calculate fractal properties of the fullerene C₆₀ in a polymer composite and also to interpret evolution of disclinations.

Features of the dense palladium-based membrane filters surface morphology are studied in this work using atomic force microscopy and scanning electron microscopy methods. Element compositions of the filters are Pd₉₅Pb₅ and Pd_93.5In_6.0Ru_0.5 (hereafter numerical coefficients determine the composition in wt.%). The thickness of dense membrane filters is 50 and 70 μм, respectively. Samples from metals of high purity were made by methods of electric arc fusion in a protective atmosphere and cold rolled with intermediate vacuum annealing. Morphology of the filter surface shows differences due to the element composition of the alloys. Manifestations of cavitation in the form of micron-sized funnels were found in palladium doping with lead and the absence of such funnels for palladium alloy with indium and ruthenium. Differences in the surface roughness of the samples are shown. In the mode of contrast of lateral forces, the atomic force microscopy method determined the presence of surface areas of different hardness. The obtained results are important for the choice of material for the manufacture of membrane filters with improved performance characteristics and for the development of the elemental composition of membrane filters in order to optimize their operation in high-tech modern technological processes.

The kinetics of the sodium borohydride catalytic hydrolysis with cobalt catalysts Co₃O₄/ZnO, Co/ZnO, Co₃O₄/zeolite, Co/zeolite, Co(OH)₂, Co₃O₄, Co–B was studied and the kinetic characteristics of the process were compared with the same characteristics during the catalytic hydrolysis of ammonia borane. The concentrations of sodium borohydride and NaOH in aqueous solution in all cases were 0.064 and 0.06 M, respectively. The apparent activation energy and the rate of hydrogen evolution during the sodium borohydride hydrolysis in the temperature range 35–80°C were determined in each case. Kinetic data were processed using zero-order, first-order, and Langmuir–Hinshelwood reaction models. The apparent activation energies during the sodium borohydride hydrolysis ranged from 37.0 for Co₃O₄ to 72.6 kJ/mol for Co₃O₄/ZnO. These values exceeded similar values for the ammonia borane hydrolysis, which were in the range 26.0–47.4 kJ/mol. A higher rate of hydrogen evolution was observed during the sodium borohydride hydrolysis compared to ammonia borane when using these catalysts, except for Co–B and Co/ZnO catalysts. The maximum rates of hydrogen evolution 3510 and 3140 mL H₂ (g cat)^–1 min^–1 were observed when using Co(OH)₂ and Co–B catalysts, respectively.

Phosphoric acid ester, a typical component of commercial dispersants, affects the functional properties of Gd_1.494Y_1.494Ce_0.012Al₂Ga₃O₁₂ ceramics. In sintered ceramics, the residual phosphorus can reach up to 40–70% of the introduced amount. The admixture of phosphorus located on the surfaces of the particles activates the grain growth during sintering and leads to the formation of secondary phases of rare-earth phosphates. With increasing phosphorus concentration, the density and optical transmittance of ceramics decrease. Relatively small amount of phosphorus can improve the luminescence properties of ceramics, but large amounts can increase phosphorescence and reduce the scintillation light yield.