A review of those photonuclear studies that were carried out at Skobeltsyn Institute of Nuclear Physics of M.V. Lomonosov Moscow State University (NIIYaF) in the Department of Electromagnetic Processes and Interactions of Atomic Nuclei (DEPIAN) in a 60-year period (1960-2020) by a group of researchers headed by Boris S. Ishkhanov is presented.
Show AbstractIn this study, electron beam dosimetry was performed by measuring free radicals induced in synthesized hydroxyapatite using the EPR method. At first, synthetic hydroxyapatite (HAP) powders were synthesized using various methods and packed after weighting. After that, a 10 MeV electron beam from an electron accelerator called a Rhodotron TT200 was used to irradiate the samples at varying absorbed high doses. At ambient temperature and in air, the EPR responses of HAP samples were measured. Peak-to-peak amplitude of the EPR signal intensity variations were then created and compared to alanine and bone powder samples. The results show that the EPR responses of some HAP samples are higher than alanine and bone powder for several times in comparison with alanine and bone samples.
Show AbstractThe possibilities are analyzed for studying the yields of reactions $^{13}$C($\gamma$, p)$^{12}$B, $^{14}$N($\gamma$, 2p)$^{12}$B, $^{14}$N($\gamma$, 2n)$^{12}$N by measuring the induced ($^{12}$B, $^{12}$N)-activity with telescopes of thin $\delta E$-detectors in time intervals between electron accelerator pulses. For production of ($^{12}$B, $^{12}$N)-nuclei and registration of their decay, estimates are given taking into account the parameters of the electron beam, Ta-radiator and irradiated targets made from graphite or NH$_4$NO$_3$, as well as the parameters of scintillation $\delta E$-detector telescopes made from thin plastic plates.
Show AbstractBased on a comparison of the parameters of the projected $\gamma$-source from back Compton scattering and the known ways of monitoring the beams of $\gamma$-quanta themselves to monitor the intensity and energy spectrum of $\gamma$-quanta in their beams at this $\gamma$-source in photonuclear studies in the region from several MeV to ~40 MeV, a system of scintillation plastic and inorganic detectors, as well as a pair magnetic spectrometer, was proposed.
Show AbstractBased on the analysis of development of photonuclear reaction studding at $E_{\gamma}≲40$ MeV and the unique parameters of the Compton source of ${\gamma}$-quanta under projecting, a program of priority photonuclear research using this source is proposed. The program includes research on: structures of giant E1 resonances and pygmy resonances; cross sections for partial photonucleon reactions; nuclear resonant fluorescence; photofission; problems of astrophysics and nucleosynthesis
Show AbstractThe ($\gamma, 1n$), ($\gamma, 2n$), ($\gamma, 3n$) reactions cross sections the majority of which were obtained using beams of quasimonoenergetic annihilation photons were discussed. The significant systematic uncertainties of the experimental results far exceeding the achieved statistical accuracy were considered. The results of experiments for about 50 nuclei from $^{51}$V to $^{209}$Bi were analyzed using objective physical criteria of data reliability. It was shown that in many cases the systematic uncertainties of experimental cross sections were significant and data do not satisfy physical criteria. The experimental-theoretical method for evaluation of cross sections satisfying those criteria was described. The systematic uncertainties of several types due to shortcomings of the method of photoneutron multiplicity sorting used in experiments and specific features of neutron detectors used. The new evaluated reliable cross sections of the partial reactions and total photoneutron reaction $(\gamma, 1n)+(\gamma, 2n)+(\gamma, 3n)$ were presented.
Show AbstractAbsolute majority of data on photonuclear reaction cross sections was obtained in experiments using bremsstrahlung and quasimonoenergetic photons produced at annihilation in flight of relativistic positrons. There are significant disagreements both in absolute value and shape between the results of experiments of both types. So, the pronounced structural features are clearly observed in the cross sections obtained using bremsstrahlung but those are practically absent in the cross sections obtained on the beams of annihilation photons. The disagreements in absolute values are definitely systematic: they are directly dependent on the data retrieval method and significantly exceed the statistical errors achieved in experiments. There are also the significant disagreements between the data obtained in experiments of the same type. In combined systematic investigations of many data on various photonuclear (primarily, photoneutron) reaction, both total and partial, cross sections the possible reasons for disagreements between the results of photonuclear experiments were found out, the status of those experiments and methods of accounting and elimination of observed disagreements are discussed.
Show AbstractThe paper discusses ground state correlations (GSC) in nuclei, which are especially clearly manifested when using the formalism of quantum Green's functions (FG) and Feynman diagrams. In addition to one-particle-one-hole GSC, which appear in the well-known random phase approximation method (RPA), there exist and give a noticeable quantitative contribution THE GSCs resulting from the use of configurations that are more complex than in RPA. Namely, configurations containing phonons and configurations containing only three quasiparticles, respectively, the GSC-phon and GSC3. This last case of GSC3 is considered in detail in the present paper. It is shown that GSC3 make a significant quantitative contribution IN THE problems related to the explanation of some characteristics of low-lying excited states (phonons) and transitions between them in even-even nuclei.
Show AbstractElectron transport characteristics through a two-dimensional quantum dot array are studied using the non-equilibrium Green's function. As the structure size of the two-dimensional quantum dot array changes, abundant meaningful electron transport properties are obtained. For a two-dimensional four-quantum-dot structure, an anti-resonance point gradually evolves into an anti-resonance band with the increase of the dot-lead coupling strength. An anti-resonance band emerges in the conductance spectrum as the energy levels of quantum dots in upper and lower quantum dot arrays are different and small. In contrast, the anti-resonance band evolves into a resonance band as the difference between the energy levels of quantum dots is large. Based on this property, the system can be designed as an efficient quantum switch. Moreover, typical Fano resonances may be observed in the two-dimensional quantum dot array. It is expected that these findings will contribute to the design of quantum devices.
Show AbstractWe use first-principles calculations density-functional theory to investigate the S-site substitution effects on the structural and electronic properties in monolayer MoS2 by O, Se and Te. The calculated structural parameters show that the changed bond lengths are caused by the different electronegativity and atomic radius. The obtained formation energies indicate that the O doping is exothermic, but the others dopings are endothermic. The electronic structures show that there is a direct-indirect band gap transition from pure monolayer MoS2 to chalcogen-doping monolayer MoS2. Moreover, the partial density of states is also calculated and analyzed.
Show AbstractHexagonal silicon polytypes are attracting much attention from the scientific community due to their potential use in next-generation electronics and photonics. However, obtaining stable heterostructures based on cubic and hexagonal polytypes is a complicated task. In the present work, the possibility of formation of hexagonal silicon of the 9R-Si phase using the traditional method of microelectronics, i.e. ion implantation, is shown. Implantation of Kr+ ions was carried out through a SiO2 layer, the thickness of which was approximately twice the projected range of Kr+ followed by high temperature annealing. It is shown using high-resolution transmission electron microscopy that a thin amorphous layer forms in a Si substrate at the interface with the SiO2 film after implantation, upon recrystallization of which the formation of the 9R-Si polytype occurs during annealing. It is assumed that mechanical stresses are created during implantation through the oxide layer, which contributes to hexagonalization during high-temperature annealing. The dependence of the efficiency of hexagonalization on the substrate orientation is established. In addition to the formation of the 9R-Si phase, at the implantation and annealing parameters used, light-emitting defects are formed in silicon, the photoluminescence of which at a wavelength of ~1240 nm is observed up to a temperature of ~ 120 K. The obtained results can stimulate and expand the range of applications of ion-irradiated silicon in micro-, nano-, and optoelectronics.
Show AbstractThe article is devoted to the problem of recovering gaps in the data series of experimental long-term continuous high-frequency observations of carbon dioxide concentration and air temperature. The study was carried out on the example of the results of observations of an automatic ecological and climatic station located in a tropical monsoon forest on the territory of south Vietnam (Dong Nai Nature Reserve). Omissions in the series of observations, as a rule, are random and are caused by technical malfunctions of the instrument base. Correctly recovered series of observations allow us to estimate the temporal variability of the observed parameters on different time scales. Within the framework of this study, options for recovering the continuity of time series based on the methods of mathematical statistics - autoregression (ARIMA) and the method of linear prediction were considered. A comparative analysis of the accuracy of restoring omissions by various methods is given.
Show AbstractIn this paper, the chemical equilibrium of a multicomponent solution is considered in detail as part of a dynamic model of the acid retardation method. A detailed study of the chemical equilibrium, represented as a system of nonlinear equations, is a key step for building an effective dynamic model in the case of a multicomponent solution. This paper presents an algorithm for efficient calculation of chemical equilibrium using extractive phosphoric acid as an example. This algorithm can be used in a dynamic model to calculate chemical equilibrium at each point of the spatial grid and at each integration step. Moreover, for the concentrations of substances in the experiment on the purification of extractive phosphoric acid, it is shown that the nonlinear system of equations of chemical equilibrium allows one to obtain simple algebraic relations for the connection of the concentration of molecules of the substance with the total concentration of substances of all elements in solution with good accuracy. In addition, it was shown that for each metal, only one type of salt sorption can be considered due to the low concentration of other types, which makes it possible to reduce the number of differential equations in the dynamic model of the acid retardation method.
Show AbstractIn the paper we present the angular distributions of photo\-electrons in ionization of neon atom by a field of several multiple frequencies. The considered setup is refered to the RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) spectroscopy under condition that the field frequencies are selected in such a way that resonant transitions through discrete states play an important role. The role of the phase of the seed infrared field on the angular distributions of photoemission is analyzed. A significant difference in the anisotropy parameters at the near-threshold sideband caused by transitions through discrete states is shown. Two methods are compared: numerical solution of rate equations with continuum discretization and third-order perturbation theory.
Show AbstractIn the present work, expressions for the system parameters that realize the maximum of the scattered field in the Mie problem separately for metals and for dielectrics were obtained. For metals, the answer was obtained in the form of formulas, for dielectrics an algorithm that allows finding the coordinates of the maximum is presented. The behavior of the solution, applied to real substances (Al, Au, GaP), is considered. In the case of the metals under relatively low dissipation at the resonant frequency, it accurately points to the maximum, and as the dissipation increases, it points to the neighborhood of the maximum. For considered dielectrics it was shown that theoretically predicted maximums are unattainable due to the limited value of the refractive index of the substance, the reasons why the maximums exist despite the mentioned limitation. In particular, it was found that the wavelength of the incident radiation and the radius of the particle at the maxima for GaP coincide with the resonance value for the internal coefficients. It was the starting point of the present study. Obtained results show that it really provides a guideline for searching for the maximum of the field scattered by other dielectrics spherical particles with a relatively low refractive index.
Show AbstractThe MATLAB program was developed to estimate composition of the asteroid material. The program models reflectance spectra of asteroids using reflectance spectra of meteorite analogues. Modeling results and estimation of the material composition for 10 asteroids (1 Ceres, 4 Vesta, 51 Nemausa, 65 Cybele, 102 Miriam, 250 Bettina, 266 Aline, 379 Huenna, 704 Interamnia, 1474 Beira) are discussed. A good agreement between the model spectra and the asteroids reflectance spectra is achieved for a number of asteroids (1 Ceres, 4 Vesta, 51 Nemausa, 250 Bettina, 704 Interamnia).
Show AbstractThe process of ionization-recombination of gas and charging of dust particles under the action of X-rays under space plasma conditions is considered. The conditions are found when, as a result of exposure to radiation, dust particles in a protoplanetary disk can acquire a positive charge even with low gas ionization.
Show AbstractThe anticorrelated distributions of temperature and density of protons are a well-known property of the solar wind. Nevertheless, it is unclear till now if they are formed by some kind of the universal physical mechanism? Unfortunately, a straightforward comparison of the characteristic relaxation times for temperature and density, on the one hand, and pressure, on the other hand, encounters the problem of inapplicability of the hydrodynamical approach in the situation when the free-path length of protons is considerably greater than the spatial scale of the structures under consideration. To resolve this problem, some kinds of the MHD turbulence - reducing the effective free paths - are usually assumed. In the present paper, we use an alternative approach based on the electrostatic (Langmuir) turbulence, described by the mathematical formalism of the spin-type Hamiltonians, which was actively discussed in the recent time in the literature on statistical physics. As follows from the corresponding calculations, formation of the anticorrelated distributions of temperature and density is a universal property of the strongly-nonequilibrium plasmas governed by the spin-type Hamiltonians when they gradually approach the thermodynamic equilibrium. So, just this phenomenon could be responsibly for the anticorrelations observed in the solar wind.
Show AbstractWithin the framework of a three-layer quasi-geostrophic model, a numerical study of the effect of an isolated submarine obstacle on the movement of surface and subsurface patches of a neutral admixture transfered by a vertically homogeneous zonal current was carried out. The possibility of partial capture of impurities by quasi-stationary topographic eddy in the vicinity of the submarine obstacle is shown. The role of the initial location (both horizontally and vertically) on the resulting pollution distribution pattern is revealed.
Show AbstractThe paper investigates the effect of a film of natural dust deposited from the air on the generation of gravitational-capillary wind waves with a length of λ<0.06 m. It is shown that with an increase in the deposition time of hydrophobic dust particles on the water surface, the contact wetting angle between the water surface and the hydrophobic particle increases, which indicates an increase in the surface tension coefficient. At the same time, the time of convergence of hydrophobic particles increases. It was found that with increasing film concentration for a given wind speed, the length of the wind wave in the generation zone decreases, and the steepness increases, which is associated with an increase in roughness and coefficient of friction at the interface. Nonlinear plane waves with a steepness of 0.13 <ak<0.25 arise in the generation zone. A method for calculating the phase velocity of such waves has been obtained and verified. The critical value of the wind speed at which the generation of wind waves begins decreases with an increase in the concentration of the dust film, and the values lie in the range 2.3 < Umin < 3 m/s.
Show AbstractA comparative analysis of mutual changes in temperature and aerosol content in the atmosphere was carried out by the data of Antarctic ice cores obtained at the Russian Vostok station and within the framework of the international EPICA project for the past 800,000 years. According to the results of cross-wavelet analysis for the last hundreds of thousands of years, variations in the content of aerosol in the atmosphere, as well as in the content of greenhouse gases CO$_2$ and CH$_4$, are generally lagging relative to temperature changes for the glacial cycles that dominated within the past million years with periods of about 100 thousands years associated with change in the eccentricity of the Earth's orbit around the Sun. At the same time, for shorter-term glacial cycles, opposite effects appear at certain time intervals with a delay in temperature variations relative to variations in the content of radiatively active components in the atmosphere, including marine and continental (dust) aerosol . In particular, the delay of temperature variations with respect to variations in the content of aerosol in the atmosphere (as well as with respect to variations in the content of methane in the atmosphere) manifests itself for modes associated with the obliquity changes with periods of about 40 thousands years.
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