Showing papers in "Bulletin of The Russian Academy of Sciences: Physics in 2017"

Mössbauer study of products of the thermocatalytic treatment of kerogen-containing rocks

Abstract: To understand the mechanism of highly efficient catalyst formation from precursors, the active form of an iron-containing catalyst and kerogen samples from the Bazhen formation are studied by Mossbauer spectroscopy and X-ray diffraction analysis. It is established that as a result of phase changes, the multicomponent precursors are transformed into mixed transition metal oxides. It is found that the thermocatalytic effect on pyrite-containing kerogen leads to the formation of pyrrhotite FeS1 − x and mixed oxides of iron.

Preliminary results from the TUS ultra-high energy cosmic ray orbital telescope: Registration of low-energy particles passing through the photodetector

Abstract: The TUS telescope, part of the scientific equipment on board the Lomonosov satellite, is the world’s first orbital detector of ultra-high energy cosmic rays Preliminary results from analyzing unexpected powerful signals that have been detected from the first days of the telescope’s operation are presented These signals appear simultaneously in time intervals of around 1 μs in groups of adjacent pixels of the photodetector and form linear track-like sequences The results from computer simulations using the GEANT4 software and the observed strong latitudinal dependence of the distribution of the events favor the hypothesis that the observed signals result from protons with energies of several hundred MeV to several GeV passing through the photodetector of the TUS telescope

Possibility of determining microimpurities in materials using a activation measuring complex based on a photoneutron source

Abstract: An activation measuring complex containing a W–Be photoneutron source of neutrons and a lowbackground gamma spectrometer is designed at the Russian Academy of Sciences Institute for Nuclear Research. The photoneutron source is mounted on the beam of a LUE-8 industrial electron linear accelerator with an electron energy of 7–8 MeV and contains a tungsten bremsstrahlung target, a photoneutron beryllium target, and a fast neutron moderator. The measuring component of the complex includes a detector made from high purity germanium, positioned inside a low-background chamber with active-passive protection. Neutron-activation analysis (NAA) is used to determine the content of microimpurities in a substance. A procedure for measuring ultralow contents of elements in aerosol filters is developed. Contents of Au, As, Sb, Mn, Fe, W, and other elements are measured in a variety of samples. The limits of detecting microimpurities in materials are estimated.

Preparation and optical characterization of nanocomposites with semiconductor colloidal quantum dots

Abstract: A simple and effective technique for depositing thin films of semiconductor colloidal quantum dots (QD) on glass substrates is developed. Samples with CdSe/CdS/ZnS quantum dots are fabricated and investigated via luminescence microspectroscopy. Four-wave mixing signals are recorded at room temperature in a solution and in a thin film of quantum dots.

Polarization-preserving anisotropic mirror on the basis of metal–dielectric nanocomposite

Abstract: The model of a polarization-preserving anisotropic mirror is proposed. The mirror is a plane boundary of a metal–dielectric nanocomposite that consists of silver spheroidal nanoparticles dispersed in a transparent matrix. The dependence of reflection spectra on the shape of the nanoparticles is studied. It is shown that in one region of the spectrum, the mirror preserves the sign of polarization in the reflected light.

Fragments in heavy ion collisions in a hydrodynamic approach with a nonequilibrium equation of state

Abstract: A hydrodynamic approach with a nonequilibrium equation of state is used to describe heavy ion collisions at medium energies. This approach includes describing the compression, dilution, and freeze-out stages of a hot spot formed during a heavy ion collision. The calculated energy spectra of protons and light 4He, 7Li, 9Be fragments produced in the 14N + 124Sn reaction at a 14N ion energy of 32 MeV/nucleon are compared to experimental data.

The Tunka-Grande experiment: Status and prospects

Abstract: The Tunka-Grande scintillation array is described. The first results from its operation are presented. The prospects for studying primary cosmic rays in the energy range of 1016 to 1018 eV during simultaneous registration of the Cherenkov and charged particle components along with radio emissions from extensive air showers are discussed.

Using accelerated electron beams for the radiation processing of foodstuffs and biomaterials

Abstract: The Department of Accelerator Physics and Radiation Medicine of Moscow State University’s Faculty of Physics conducts experiments on the radiation processing of food products and the development of a new technology for the combined sterilization of bone implants, based on the joint action of different sterilizing factors (radiation and sterilization) in a gaseous medium. Radiation processing of potato tubers and bone implants is performed using accelerated electron beams with energies of 1 MeV. The results from experimental investigations along these lines are presented.

Mathematical simulation of few-nucleon experiments with three or more particles in the final state

Abstract: A computer program for the kinematic simulation of nuclear reactions with three or more particles in the final state is described. Simulation results for the d + 2H → (nn)S + (pp)S → p + p + n + n reaction, which proceeds through the formation of a singlet dineutron and diproton in the intermediate state, are presented as an example. It is shown that the kinematic parameters of breakup particles depend on the parameters of the intermediate state. The results from simulating secondary neutron spectra are compared to an experimental neutron time-of-flight spectrum obtained in a kinematically complete experiment at a deuteron energy of 15 MeV. As a result of the comparison, the energy of the quasi-bound singlet 1S0 state of the 2n-system is determined.

On-site observations of seismoacoustic waves under the conditions of an ice-covered water medium

Abstract: Patterns of wave disturbance propagation in nonuniform media, including the layered Earth, a liquid waveguide, and a covering ice layer are studied. The velocities of different modes are estimated based on the cross-correlation function for signals set in two spatially spanned points. Experimental data are compared to numerical modeling results.

Comparative study of deep structures by means of passive microseismic sounding and seismic tomography

Abstract: Modern surface wave–based approaches to the deep sounding of the Earth are compared, along with results from reconstructing deep structure of the Hawaiian plume, obtained by phase and amplitude methods. Ways of further improving these methods are proposed.

Activation measurements of the integral cross sections of reactions 7Li(p, n 0 + n 1)7Be g.s. , 6Li(d, n 0 + n 1)7Be g.s. , 7Li(d, 2n)7Be g.s. , 65Сu(p, n)65Zn, 65Сu(d, 2n)65Zn, and 63Сu(d, γ)65Zn

Abstract: Cross sections of reactions 7Li(p, n 0 + n 1)7Beg.s., 6Li(d, n 0 + n 1)7Beg.s., 7Li(d, 2n)7Be g.s., 65Сu(p, n)65Zn, 65Сu(d, 2n)65Zn, and 63Сu(d, γ)65Zn are measured on the EGP-10 electrostatic tandem accelerator at the All-Russia Research Institute of Experimental Physics by means of activation at proton (deuteron) energies of 2–10 MeV. The technique for making targets and calculating LiF layer thickness is described. Target irradiation, measuring the efficiency of γ-quanta registration, and a procedure for measuring the cross sections of reactions are discussed and their measured values are presented.

Experimental quantum cryptography with single photons

Abstract: Results are presented from experimental and theoretical studies of the dependence of the rate of quantum key distribution on the average number of photons in a laser pulse. The experimental data are obtained using atmospheric and fiberoptic experimental setups for a quantum key distribution based on the BB84 protocol.

Linear organic–inorganic heterometallic copolymers [(Fe, Zn)(H2O)3{NH(CH2PO3H)3}] n and [(Fe, Cd)(H2O)3{NH(CH2PO3H)3}] n : The missing link in the mechanism of inhibiting local steel corrosion with phosphonates

Abstract: Heteropolynuclear [Zn0.5Fe0.5(H2O)3{NH(CH2PO3H)3}] n and [Cd0.125Fe0.875(H2O)3{NH(CH2PO3H)3}] n complexes, which form during interaction between inhibitors of corrosion and Fe2+ ions and play an important role in inhibiting local steel corrosion by complexes of nitrilotrismethylenephosphonic acid, are isolated for the first time. Their composition, structure, and properties are studied by means of XSA, EDRS, IR and Raman spectroscopy.

Cosmic rays, solar activity, and changes in the Earth’s climate

Abstract: One of the most important problems facing humanity, global climate change, is discussed. The roles of cosmic ray fluxes and solar activity in this process are analyzed. Although several mechanisms explaining global climate change have been proposed, none of them are firmly grounded. At the United Nations summit in Paris at the end of 2015, it was decided that greenhouse gases are responsible for the global warming of our planet. However, the authors of this work believe the question of what causes global changes in the Earth’s climate remains open, and will obviously be solved once and for all in the next 10–15 years.

Cross sections of the photoneutron reaction for 141Pr and 186W nuclei, estimated from physical criteria of data reliability

Abstract: Using objective physical criteria for data reliability, cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n) and (γ, 3n) that are free of the shortcomings of neutron multiplicity sorting methods used on beams of quasimonoenergetic annihilation photons are obtained for 141Pr and 186W nuclei. Evaluation is performed using the experimental–theoretical method (ETM), based on the experimental cross section of neutron yield reaction σexp(γ, xn) = σexp(γ, 1n) + 2 σexp(γ, 2n) + 3 σexp(γ, 3n) + … and ratios F i theor= σtheor(γ, in)/σtheor(γ, xn) calculated within the combined model (CM) of photonuclear reactions, which stipulates that σeval(γ, in) = F i theor σexp(γ, xn). It is found that for 141Pr and 186W, ratios F exp i do not contradict the data reliability criteria only at energies up to ~21 and ~22 MeV, respectively. At the same time, there are notable discrepancies between F i theor and F exp i, and thus between the evaluated and experimental cross sections of reactions. It is shown that the discrepancies between the evaluated and experimental cross sections are due to the assumed unreliable experimental distribution of neutrons in the channels with multiplicities 1, 2, and 3.

Precipitation of magnetospheric electrons into the Earth’s atmosphere and the electrons of the outer radiation belt

Abstract: More than 500 X-ray emission events generated by precipitating electrons from the outer radiation belt have been recorded in the Earth’s atmosphere over the many years of the Lebedev Physical Institute observing fluxes of ionized radiation. This precipitation is closely related to high-velocity solar wind streams, whose rate of occurrence, like that of precipitation events, is greatest during the decline phase of the 11-year solar activity cycle. This work considers the relationship between the high-velocity solar wind, the relativistic electron fluxes in the outer radiation belt, and the electron precipitation observed in the polar atmosphere.

Development of diocotron instability in the squeezed state of a relativistic electron beam

Abstract: Nonlinear nonstationary processes in a beam-plasma system containing a hollow intense relativistic electron beam with an overcritical current in the squeezed state are studied numerically. The emergence and development of diocotron instability in the squeezed state, which leads to formation of vortex structures, is analyzed in detail, and the effect the magnitude of the external magnetic field has on the processes of structure formation in the beam is investigated.

Effect of nonstationary regimes of the natural and mixed convection of melts on heat transfer and the forms of crystallization fronts in the Czochralski method

Abstract: Regimes of the natural and mixed convection of melts with Prandtl numbers ten and 16 are studied experimentally and numerically. The evolution of spatial shape of flow as the Reynolds number rises is studied, as is that of heat transfer on the crystallization front at fixed values of the Grashof and Marangoni numbers, relative to the crystal radius. The boundaries of transitions to nonstationary flow regimes are determined.

Surface tension of copper in solid phase

Abstract: Literature data on the surface tension of copper σs in the solid phase are reviwed. The σs values obtained by different researchers using the zero creep method are given. The most reliable result is an σs obtained by the zero creep compensation method in vacuum. At 1253 K, it is (1520 ± 14) × 10−3 J m−2.

Mössbauer spectroscopy of grain boundaries in ultrafine-grained materials produced by severe plastic deformation

Abstract: The applicability of Mossbauer spectroscopy in studying grain boundaries in ultrafine-grained materials produced by severe plastic deformation (SPD) is analyzed. It is shown that grain boundaries after SPD are in a nonequilibrium state that is characterized by excess free volume.

Acceleration of particles and generation of nonthermal emission in old supernova remnants

Abstract: Particle acceleration by shock waves in old supernova remnants is studied. The radiative loss of gas behind the front of a shock wave, the streaming instability of magnetohydrodynamic waves, and the damping of waves on neutral atoms are considered. The calculated spectra of electromagnetic emissions are compared to observations of supernova remnant IC 443.

Variations in cosmic rays and the surface electric field in January 2016

Abstract: Three units of neutron detectors and four blocks of gamma-ray spectrometers have been installed and started operation at Complejo Astronomico El Leoncito, CASLEO (San Juan, Argentina; coordinates 31 S, 69 W; height of 2550 m; the rigidity of geomagnetic cutoff of R c = 9.7 GV) in May 2015 as part of the scientific cooperation between the Lebedev Physical Institute, Russian Academy of Sciences (Moscow, Russia), Universidade Presbiteriana Mackenzie (San Paulo, Brazil) and Complejo Astronomico El Leoncito, CASLEO (San Juan, Argentina). Measurements with the new detectors greatly supplement the experimental data on variations in the charged component of cosmic rays obtained by the CARPET ground-based cosmic ray detector in 2006. The first results from a joint analysis of new experimental data are presented. Particular attention is given to growing cosmic ray fluxes associated with changes in the surface electric field. The main characteristics of the events recorded in January 2016 are presented.

The exhaustive search for optimum minimum peak sidelobe binary sequences

Abstract: The problem of designing binary sequences with the minimum sidelobe level of the aperiodic autocorrelation function is considered. The results from searching for the optimum minimum peak sidelobe binary sequences in the range of lengths N = [83;84] are presented. Examples of binary sequences with sidelobe level PSL = 5 having the higher value of the MF coefficient are presented for lengths N = [83;88].

Analyzing the June 2015 Forbush effect by the spectrographic global survey

Abstract: The June 2015 Forbush effect is studied using ground-based measurement data on cosmic rays (CRs), obtained from the worldwide network of stations by the spectrographic global survey. When approximating the variation spectra via the exponential function of particle rigidity in the 10–50 GV range, the spectrum index is higher at the phase of maximum modulation than at those of the drop in CR intensity and its recovery.

Formation of a martensitic twins structure in Ni2.16Mn0.84Ga heusler alloy by high magnetic fields under adiabatic and isothermal conditions

Abstract: The results are presented from experimental studies of the formation of martensitic twin structures in Ni2.16Mn0.84Ga Heusler alloy under the effect of magnetic fields of up to 14 T using a specially developed optical microscope under isothermal and adiabatic conditions. A qualitative model is proposed that explains the differences between the progress magnetoinduced magnetostructural first-order phase transitions under different thermodynamic conditions.

Searching for stimulated de-excitation of the 186m Re nuclei isomeric state in ISKRA-5 laser plasma

Abstract: Several targets containing 186mRe isomeric nuclei are irradiated by laser pulses with an energy of 300 J and a duration of 0.3 ns at the ISKRA-5 facility. The results from measuring the γ-spectra of irradiated samples indicate the stimulated de-excitation of a fraction (~10–7) of the 186mRe nuclei in the laser plasma.

The Carpet-3 experiment to search for diffuse gamma rays with energies of more than 100 TeV

Abstract: An experiment for measuring the flux of cosmic diffuse gamma rays with energies above 100 TeV (the Carpet-3 air shower array) is now being prepared at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. The preparations entail a substantial increase of the areas of both the muon detector and the surface air shower array. The experiment’s sensitivity to showers generated by primary gamma rays is estimated for different configurations of the array. In addition, preliminary estimates of the upper limit on the flux of diffuse gamma rays with energies higher than 1.3 PeV, derived using experimental data from the old Carpet-2 array, are presented for a net exposure time of 9.2 years.

Quantum scattering by nonspherical objects

Abstract: The problem of scattering by spherically asymmetric potentials is considered where angular momentum not only ceases to be a conserved quantity but is also not a convenient basis for the expansion of wave functions and scattering amplitudes. Numerical solutions of the two-dimensional differential equation for the scattering amplitude of a particle and a coupled pair on a semitransparent disc of finite thickness are obtained. The effect of resonant diffraction is shown. A numerical scheme can be used to describe the scattering of a particle by deformed atomic nuclei.

Magnetic Properties of Chain Antiferromagnets RbFeSe2, TlFeSe2, and TlFeS2

Abstract: Single crystals of ternary ion chalcogenides RbFeSe2, TlFeSe2, and TlFeS2 are studied by X-ray diffraction, SQUID magnetometry, and Mossbauer spectroscopy. Common structural units of these chalcogenides are tetrahedra of FeCh4 (chalcogen Ch = Se, S), arranged in chains by sharing an edge. It is found that RbFeSe2, TlFeSe2, and TlFeS2 undergo transition to a collinear antiferromagnetic state below temperatures T N = 248, 290, and 196 K, respectively. Their magnetic moments are oriented perpendicular to the axes of the chains of FeCh4 tetrahedra.