Journal of Contemporary Physics (Armenian Academy of Sciences)最新文献

A simple quantum chain with a topological phase is constructed. It is formed by parafermions (quasiparticles obeying the fractional statistics) with angular parameter (theta = {{2pi } mathord{left/ {vphantom {{2pi } 3}} right. kern-0em} 3}). The model is derived from the one-dimensional spin model with topological order protected by the ({{mathcal{Z}}_{3}} times {{mathcal{Z}}_{3}}~) symmetry (generalized cluster model). Parafermionic zero modes arising at the chain boundaries, which remain stable because of the vacuum gap and topological order, are constructed and studied.

Samples of natural zeolite from the Nor-Kokhb deposit (Armenia), activated with zinc oxide (30% ZnO) and silver (30% ZnO + 5% Ag), were studied during chemical and thermal treatment by microwave and traditional methods. It was previously shown that microwave processing is 3 times faster than the traditional method. The X-ray diffraction analysis shows the presence of zeolite in the form of clinoptilolite and zinc oxide in the studied samples. Based on the results of optical and EPR spectroscopy, the presence of Fe³⁺ ions in the framework and extra-framework positions of the zeolite of the studied samples was revealed. The study of diffuse reflectance spectra showed that in zeolite, which is a wide-gap material (with a band gap of 4.14 eV), the activation of 30% ZnO decreases the band gap to 3.38 eV, and with additional activation with a silver (30% ZnO + 5% Ag) the bandgap decreases to 3.31 eV. The photocatalytic activity of natural zeolite activated with zinc oxide (30% ZnO) and silver (30% ZnO + 5% Ag) was studied according to the decomposition reaction of methylene blue under UV irradiation.

In the presence of the axial magnetic field, the behavior of the electron in the colloidal CdSe nanoplatelet containing multi-impurity centers has been investigated. The two-dimensional Schrodinger equation with the effective potential of the interaction of electron and impurity centers, localized in the central plane of the nanoplatelet has been obtained. It has been shown that the magnetic field influence on the electron energy levels weakens with increasing the number of impurities.

The article presents the results of studies of the characteristics of lead tungstate crystals (PbWO₄). Measurements of light transmission and light output from the passage of cosmic muons were carried out. The average light transmittance of crystals in the transverse direction is 62.82, 68.38, and 75.68% at wavelengths λ = 360, 420, and 620 nm, and the light output is ~16 pe/MeV. A prototype of an electromagnetic calorimeter was designed and built from crystals arranged in a 4 × 4 matrix which has been tested by cosmic muons. The results obtained confirm the conclusions of other groups in the Electron-Ion Collider collaboration that the quality of the crystals produced by CRYTUR meets the requirements for an electromagnetic calorimeter, and that they can be the basis for its creation.

The results of the studies on the production of ¹⁵⁵Tb isotope, which is used in theranostic applications for oncological diseases, utilizing the proton beam of the medical cyclotron C18/18 are presented. The measurements of the induced activity were carried out using the activation method, followed by spectrometric analysis. Natural gadolinium was used as the main target. Excitation functions were calculated for the ^natGd(p, xn)¹⁵⁵Tb reactions using TALYS 1.96 and EMPIRE 3.2 theoretical nuclear codes. The measured cross-section values were compared with the results of the theoretical calculations as well as with the experimental data from other works. The experimental value of the integral activity of the radionuclide ¹⁵⁵Tb was compared to the results obtained with the TALYS 1.96 code and with early published data.

The wettability of black silicon (b-Si) layers formed by reactive ion etching, metal-assisted chemical etching, and laser-induced etching has been studied. The wetting contact angles of the prepared samples with deionized water, glycerol, diiodomethane, and ethylene glycol were determined. It has been shown that the silicon oxide surface film and the enlargement area factor of b-Si layers have a significant influence on their wettability, varying from hydrophilic to hydrophobic properties.

Locally inclined targets are developed to produce medical radioisotopes which can be used for high-intensity proton beam irradiation. The results of a numerical analysis of thermal processes in locally inclined targets made of pressed molybdenum powder with a niobium target holder for the Nirta Solid Compact Model TS06 target module are presented. Computations were carried out using the Fluid Flow (Fluent) engineering package of the ANSYS Workbench 18.2 software platform for variants of targets with linear and axially symmetric grooves in the proton irradiation zone. It has been shown that using various models of locally inclined targets with a cooling area increased by 2.37 times, it is possible to increase the irradiation current by 1.34–1.46 times compared to a standard flat target. An analysis of the distribution of heat flows and temperatures in the targets was also carried out.

The work presents a study of the parameters of secondary X-ray radiation generated during the operation of a sterilization setup based on a high-current pulse-periodic electron accelerator, SINUS-320. The energy of accelerated electrons equals to 500 keV. Therefore, the issues of radiation protection during the operation of the installation are highly topical, which results in the importance of studying the energy spectrum and dose rate of the secondary X-ray radiation. The studies were carried out by statistical simulation using the GEANT4 toolkit.

Based on a detailed numerical analysis and comparison with experimental observations, a nonlinear process of the generation of a new type of similaritons in fibers is presented in the region of negative dispersion. These similaritons are needle-like in shape with a sharp top and a large base and are formed in passive single-mode optical fibers with weak nonlinearity and strong group velocity dispersion. Consistent boundary conditions are found for the parameters of the input pulse and the characteristics of the optical fiber under which such self-similarly propagating pulses are generated.

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.