The possibility of improving the quality of X-ray images formed using diffraction on a two-block crystalline system is considered. It is shown that the low spatial coherence of the initial radiation improves imaging quality. Conventional wide-focus X-ray tubes can be used as a source for such radiation. The feasibility of using a scanning scheme to reduce the background level in the formed image was also considered by numerical simulation.
The SiO2/ZnO nanocomposite with a core-shell structure for photocatalysis from water-soluble zinc salts and sodium silicate was synthesized using the hydrothermal-microwave method. The physicochemical properties of the synthesized SiO2/ZnO were studied and its photocatalytic activity was tested. The band gaps of the heat-treated composite (E_{{text{g}}}^{{{text{dir}}}}) and (E_{{text{g}}}^{{{text{indir}}}}) are 3.35 and 3.32 eV, respectively. The photocatalytic activity of the resulting SiO2/ZnO was determined by the decomposition reaction of methylene blue under UV irradiation. The conversion of methylene blue was determined by optical method. The resulting SiO2/ZnO has high photocatalytic activity. The conducted studies showed the effectiveness of microwave synthesis of SiO2/ZnO with a core-shell structure in comparison with traditional methods.
The oscillatory behavior of a heavy substitutional impurity (Cr3+) in Al2O3 has been studied by the Brillouin scattering method. The oscillations of chromium ions are carried out by their photoexcitation. Discrete shifts of the ruby luminescence lines R1 and R2 at room temperature depending on the absorbed laser pump power upon excitation of the 2T1 state observed for the first time. These shifts are caused by the excitation of quasi-local vibrations of chromium ions. The frequency of quasi-local oscillations is equal to 22 GHz, which corresponds to transverse acoustic oscillations in ruby. An explanation of the observed phenomenon is given based on the Born–Oppenheimer adiabatic approximation and the Pekar function.
The vacuum expectation value of the current density for a massive scalar field in a (D + 1)-dimensional flat space-time with compact dimension is investigated. Along a compact dimension, the field operator obeys the helical quasiperiodicity condition with a constant phase. The results previously studied in the literature are obtained in the special case of a zero helicity parameter. In contrast to this case, the vacuum current, in addition to the component along the compact dimension, has a non-zero component in the direction of the non-compact dimension along which the field operator is shifted. A simple relation between these components is obtained. They are odd periodic functions of magnetic flux penetrating the compact dimension, with the period equal to the magnetic flux quantum. For a given non-zero value of the helicity parameter, the component of the vacuum current along the compact dimension tends to zero in the limit when the length of that dimension tends to zero. In the problem considered earlier with the usual quasiperiodic condition, the vacuum current diverges in that limit.
This article provides data on the development and creation of a vacuum window module, which will bring out the proton beam of the C18 cyclotron (IBA, Belgium) with energy of 18 MeV from a vacuum environment into the atmosphere. The module is made of aluminum and consists of a flange with a collimator and a helium (He) chamber of foil plates cooling. The module was installed at the end of the cyclotron’s beam line. Profile measurements were made for various current values of proton beam from 1 to 30 µA. The vacuum window showed its functionality.
The use of a drone as an aerial vehicle to realize the antenna measurement method is considered. The drone is controlled by software, using unified radio-electronic equipment containing a transmitter, a half-wave vibrator, and a GPS navigator. The parameters of the directional properties of the antenna system are the result of software processing of the output signals of the radar receiver synchronized with the coordinates of the drone flight path points.
Using computer simulation, the processes of heat propagation were studied and noise was determined in a three-layer detection pixel of a thermoelectric single-photon detector, consisting of an absorber (Pt), a thermoelectric sensor (La0.99Ce0.01B6) and a heat sink (Pt, Mo). The absorption of photons with energies of 0.8–7.1 eV (1550–175 nm) in absorbers of various thicknesses, providing high absorption efficiency, was studied. The simulation was based on the heat propagation equations from a limited volume. The temporal dependencies of the signal appearing on the sensor were studied. Signal power, noise equivalent power, and signal-to-noise ratio were determined. It was shown that a detection pixel with a platinum absorber can reliably detect single photons with the energy of 3.1–7.1 eV.
Briefly presented the scientific and technical state of the linear accelerator complex of the A. Alikhanyan National Scientific Laboratory. LUE-75 after renovation work carried out in recent years. The need for further modernization of the accelerator’s main systems to ensure its long scientific life is substantiated. An analysis of the state of individual nodes and systems of the accelerator and calculations have been carried out, based on which modernization is proposed by the introduction of modern technology. The use of new-generation power electronics, vacuum equipment with a modern interface, and a thermostabilization system is offered.
The spectral features and structural factors influencing the formation of luminescence bands of Ce3+ ions in YAG:Ce crystals are considered. The energy levels of the 4f shell of Ce3+ ions occupying both dodecahedral and octahedral sites of the crystal lattice have been determined. The participation of Ce3+ ions and ({text{Ce}}_{{{text{Al}}}}^{{3 + }}) ions in the structure of the luminescence band was shown and the multicenter structure of Ce3+ ions in the 4f ↔ 5d transitions of the activator was determined.
Peculiarities of X-ray beam diffraction from potassium and rubidium bi-phthalate piezo crystals under the condition of excitation of transverse ultrasonic vibrations are investigated. Previously, under a similar influence in quartz crystals, the effect of X-ray acoustic redistribution was observed, in which the intensity of diffracted radiation in the exact Bragg position increases significantly with a simultaneous decrease in the intensity of the transmitted beam, down to zero for certain parameters for reflecting atomic planes, called the full pumping effect. This effect can be used for controlled tuning of the diffracted beam intensity. In this work, to search for new materials for the creation of elements that allow such a rearrangement, we studied the dependences of the degree of amplification of diffracted radiation on the amplitude of the control signal for potassium and rubidium bi-phthalates crystals. The actual possibility of X-ray intensity modulation using transverse vibrations in these crystals is demonstrated.
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