R e g u l a r p a p e r s

Physics of nuclei and elementary particles

Moscow University Physics Bulletin 2020. N 1.

In this work, we present our MCNP6.1 modeling of some critical fast experimental benchmarks, aiming to qualify our cross-section libraries derived from ENDF/B-VII.1, ENDF/B-VII, JEFF-3.1, JENDL-3.3, and JENDL-4.0. The analyzed benchmarks are characterized by simple geometries which helps to have taken precise results, and concerning the type: HEU-MET-FAST (Highly enriched uranium). Those benchmarks are extracted from the "International Handbook of Evaluated Criticality Safety Benchmark Experiments (IHECSBE)" published by the Nuclear Energy Agency [1]. A detailed comparison of the results of our simulation was made in order to highlight the influence of these nuclear data types on our calculations, due to its importance for the stability of nuclear reactors. We interpreted the difference between Calculation and Experiment (C – E) for the principal parameter keff through a comparison of the fission and capture rates of the major fissile elements. The different spectral indices F28/F25, F49/F25, F37/F25, C28/F25, and F23/F25 at the cores center are also calculated. For the majority of the studied HEU (Highly enriched uranium) benchmark cases, The ENDF/B-VII and JEFF-3.1 have a good agreement with the experimental ones, concerning the keff results. The average discrepancy from the experimental values for ENDF/B-VII is 0.42%, and 0.39% for JEFF-3.1. An overestimation was observed for most evaluations concerning benchmarks with Tungsten carbonate reflectors. The best results were obtained by JENDL-3.3, with a maximal discrepancy C – E estimated 0.47% concerning fission rate, and 4.25% for capture rate. In analyzing the spectral indices, for GODIVA and FLATTOP-25, the best results were obtained by JENDL-4.0 with a maximal discrepancy of 2.66%.

Show AbstractMoscow University Physics Bulletin 2020. N 1.

In this paper, a simple procedure of exceptional geometrical form simulation is designed by using GATE (Geant4 Application Tomography Emission) software packages. The phantom used, has an unusual geometry, which makes the acquisition of images and their reconstruction more complicated. The results obtained show that Signal-to-Noise Ration (SNR) of sinograms and images, resolution spatial and lines profile are almost perfect.

Show AbstractMoscow University Physics Bulletin 2020. N 1.

There are many research reactors around the world that have been installed from many years ago and must be decommissioned sooner or later. Most of these reactors were fuelled with high enriched uranium and substantial amount ofinitialloaded fuel has not been exploited yet. The reactor conversion to an Accelerator Driven System (ADS) is one of the novel ideas for minor actinide utilization and reducing the spent fuel radio toxicity.The main objective of this study is dedicated to spallation target design in Miniature Neutron Source Reactor (MNSR) core conversion to an ADS one.The MNSR is a pool type research reactor, which was developed by china and installed in Isfahan nuclear technology center in 1994. After more than 25 years, the fuel burn-up could not be compensated more by adding shimming plates. The sub-criticality in MNSR reactor was attained by entirely removing the top plate shims as well as control rod and installing the spallation targetin interior space ofguide thimble. Different state of the art targets such as Tungsten, Lead, Bismuth, and LBE have been investigated and targetneutronic parametersincluding the spallation yield, neutron energy spectrum, deposited energy and the angular distribution of spallation neutronswere evaluated using MCNPX2.6 code. The results showed that the neutronic performance of Tungsten is somewhat greater than its competitors. On the other hand the maximum power density in Tungsten is about two times greater than Lead and LBE targets.

Show AbstractMoscow University Physics Bulletin 2020. N 1.

Gamma irradiation technology plays a very important role in the development of agriculture, due to its various advantages, such as the inhibition of germination, the appearance of new varieties, preservation...etc. To properly control and characterize irradiation operations, the dose rate distribution in the irradiation cells must be well controlled, The Monte-Carlo method was used for experiments the high cost to map the dose rate distribution in the irradiation cell each time, and to its precise dosimetric calculation. In this study the MCNPX code was used to simulate the irradiation cell of the National Institute of Agricultural Research (NIAR) of Tangier Morocco, the validation of the latter was based on a comparative assessment between the dose rates absorbed in the area calculated by MCNPX (Gy/min) and those measured values by alanine dosimeters. The comparative results showed a good agreement between the experiment and the simulation

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The spectroscopic amplitudes of the virtual decays of 28 (30) Si isotopes 28 (30) Si (JB) - p (t) + 27Al (JA) were obtained using the wave functions of 1d - 2s shell nuclei in Nilsson model. It has been shown that using of corrective spectroscopy of 1d-2s shell nuclei and accounting their deformation affect on the spectroscopic amplitudes values and signs of both the proton and triton.

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Back-bombardment effect is studied by the example of the 10MeV standing wave technological electron linac. The beam dynamics are calculated, the spectra of backstreaming electrons are obtained, the power released by the backstreaming electrons at the cathode was estimated. The observed effects are in good agreement with the calculations.

Show AbstractTheoretical and mathematical physics

Moscow University Physics Bulletin 2020. N 1.

The problem of the construction of shock waves by the method of boosting the metricsof black holes and bare singularities is considered. It is noted that when boosting, singularterms may arise that prevent the generation of shock waves, in particular, in the absenceof quasi-Cartesian coordinates. When boosting the Fisher metric of a black hole with ascalar charge and a singular horizon, it is found that the scalar field disappears as a resultof boosting, unlike the case of black holes with electric and magnetic charges. It is noted17 that boosted metrics are solutions of the linearized Einstein equations, while the originalmetrics are exact nonlinear solutions of these equations. When boosting, the event horizondisappears, so boosting of naked singularities leads to the same result as boosting blackholes. This is also confirmed by the example of gamma-metrics (Zipoy-Vourhees solution).Finally, it is shown that when a linearized metric is boosted with the Newman-Unti-Tamburino parameter (NUT) along the Misner string, a shock wave with a non-diagonalstructure of the gyraton is obtained.

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We calculate the power and probability of electron radiation in a constant background tensor field violating Lorentz invariance. The angular distribution and polarization of radiation are investigated. Using modern experimental restrictions on the background field strength, it is shown that the radiation effect can manifest itself under astrophysical conditions at ultrahigh electron energy.

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In this work, we have found a solution to the Einstein equations for a closed null string with axial symmetry, which radially increases its size. The possibility of choosing the ideal gas of null-strings as a dominant source of gravity is confirmed in the study of the null-string inflation mechanism in Friedman-Robertson-Walker spaces. The absence of a limit transition between the solution found and the solution for a closed null string in shape of a circle that changes its size radially is shown. This indicate a stability of configuration of a closed null string in shape of a circle during motion in an external gravitational field. It has been noted that a part of characteristics of null string gas, such as an ability to form a domain structure and an existence of stable polarized states (multi-string systems), does not depend on a shape of a null-string, but the dynamics of a test null string in a field of such a multi-string system will have peculiarities.

Show AbstractMoscow University Physics Bulletin 2020. N 1.

When studying light-sensitive or rapidly evolving objects the number of illumination photons interacting with the object is often low, which causes poor quality of the reconstructed image of the research object. In this situation the mathematical techniques of measurement data processing should not only provide minimal error, but also use all available information about the research object for further reduction of the error. The source of information that is used alongside measurement data to estimate the distribution of the optical characteristics of the object could be researcher's notions about the possible form of the distribution of characteristics of interest of the research object and about the plausible noise realizations. The article considers a version of the mathematical method of measurement reduction that allows to use such information, which is modeled using the mathematical formalism of subjective modeling, and to verify using measurement data their concordance with the subjective information provided by the researcher.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2020. N 1.

A method for increasing sensitivity of electrical field detection is proposed for scanning probe microscopy technique in which the distribution of the surface potential is measured simultaneously with the topography using a field-effect transistor with a nanowire channel for the case when the surface of the sample is covered by a dielectric layer that strongly attenuates the electric field of the detected electric charges. The method consists in deposition (using electron-beam physical vapor deposition) of additional resistive (Rsquare > 10kOm) chromium film of 5nm thick over a dielectric layer. Such film consists of small chromium granules separated by tunnel barriers. It was experimentally shown on the fabricated test structures that the method allows to restore the signal attenuated by the dielectric layer by 70 - 80%. The estimates showed that the sensitivity threshold of transistors integrated into the scanning probe microscope cantilever is within 2-5 mV in a single frequency band at a frequency of 100 Hz.

Show AbstractOptics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2020. N 1.

The results of studying the IR absorption spectra under the condition of impaired total internal reflection of 1,2-dichloroethane and 1,1,2,2-tetrabromoethane in porous glasses with different pore radii are presented. The changes in the intensities of the trans and gauche conformations in the studied systems were determined for different pore radii of glass R. The dependences of the differences of the free energies of trans and gauche conformations for 1,2-dichloroethane and 1,1,2,2-tetrabromoethane on the pore radius of porous glass were obtained. At R > 3.5 nm, an increase in the number of g-conformers is observed for 1,2-dichloroethane, while an increase in the number of t-conformers is observed for1,1,2,2-tetrabromoethane . Keywords: IR spectra, porous glasses, trans-, gauche conformation, 1,2 - dichloroethane, 1,1,2,2, -tetrabromoethane, free energy of conformation.

Show AbstractPhysics of Earth, atmosphere, and hydrosphere

Moscow University Physics Bulletin 2020. N 1.

The results of mathematical modeling of pollutant transport in the Selenga River shallow water of Lake Baikal during the autumnal thermal bar evolution are presented. Analysis of the spatial distributions of pollutant at various wind scenarios was conducted. Numerical experiments demonstrated that during the cooling of shallow water the structure of impurity concentration isolines depends on the wind direction.

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The paper describes a model of ocean waves generation by seismic movements of the bottom. A feature of the model is the use of curvilinear non-orthogonal sigma-coordinates. We used the model for studying the generation mechanisms of gravity waves excited by the surface seismic waves. The results of numerical experiments are presented in the paper.

Show AbstractMoscow University Physics Bulletin 2020. N 1.

Mechanisms of seismic sources of the Mediterranean region, not the corresponding models of sources in the form of a double dipole and describing a complex rupture in the field of a source are considered. The analysis is carried out by decomposition of an observed tensor of the seismic moment of the strongest earthquakes on components: an isotropic part (ISO), a double-couple dipole (DC) and the compensated linear vector dipole (CLVD). According to observations for the period (2000-2019), in the region there were 121 earthquakes registry with magnitude more than 5.5; from them 57 events do not correspond to model of a double-couple dipole. For these earthquakes the CLVD parameters were received and physical interpretation of results of decomposition of a tensor of the seismic moment is offered. The similar analysis is carried out for the first time. On the basis of the received results conclusions were drawn about details of the rock failure and the structure of the Earth in hypocenter zones.

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