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Issue 2, 2024

Physics of nuclei and elementary particles

Photonuclear experiments: from the bremsstrahlung to the Compton backward scattering photons

Photonuclear experiments: from the bremsstrahlung to the Compton backward scattering photons

V. V. Varlamov, A. I. Davydov

Moscow University Physics Bulletin 2024. N 2.

The features of the methods for obtaining the information on photonuclear reaction cross sections using the beams of bremsstrahlung and quasimonoenergetic photons from the annihilation in flight of relativistic positrons with which such the absolute majority of such kind data was obtained are discussed. It was shown that significant disagreements between the results of such experiments in cross sections absolute values and shapes are due to both methods definite shortcomings which to a certain extent can be overcome by using the beams of the photons from the processes of Compton backward scattering.

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The fine structure of pygmy and giant multipole resonances in nuclei

The fine structure of pygmy and giant multipole resonances in nuclei

S. P. Kamerdzhiev, M. I. Shitov

Moscow University Physics Bulletin 2024. N 2.

A brief overview of experimental and theoretical results in the field of pygmy and giant resonance energies is presented. First, E1- resonances in $^{208}$Pb, where the limit of experimental resolution in the pygmy-dipole resonance region has been reached and separate $1^-$ levels have been identified. Secondly, the most important physical results of experiments with a resolution of 50-200 keV: the significance of such experiments for gamma strength functions that determine the characteristics of nuclear reactions, and the modern physical analysis of resonance structures -- wavelet analysis -- is briefly discussed. Some results in the field of excitation energies (1-5) MeV are also discussed.

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The storage ring of the Compton source of the NCPM

The storage ring of the Compton source of the NCPM

D. A. Bobylev$^{1,2}$, V. I. Shvedunov$^{1,2}$

Moscow University Physics Bulletin 2024. N 2.

In this paper, the magnetic structure of the storage ring of an X-ray source based on the effect of Compton backscattering and designed for use in the electron beam energy range from 35 MeV to 120 MeV is investigated. For this storage ring, the results of calculating the dynamics of the electron beam are presented and the effects of radiation damping, quantum excitation, laser damping and intrabeam scattering are considered. The dynamic aperture and energy acceptance of this ring are discussed. The results of calculating the magnitude of the spectral brightness of X-ray radiation and its change over time are presented.

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Optics and spectroscopy. Laser physics

Second harmonic generation in structures with inhomogeneous magnetization distribution

Second harmonic generation in structures with inhomogeneous magnetization distribution

I. A. Kolmychek, V. B. Novikov, A. I. Maydykovskiy, T. V. Murzina

Moscow University Physics Bulletin 2024. N 2.

The study of the interaction of laser radiation with ferromagnetic materials is not only an inexhaustible source of new effects, but also provides an opportunity to study magnetic media at the micro- and macro-scale. This is especially important for the development of modern technologies to produce structures with fundamentally new magnetic and optical properties that can’t be observed in natural materials. The review presents the results of studies of nonlinear optical effects in ferromagnetic nano- and microstructures, as well as films of different compositions. The unique capabilities of nonlinear-optical diagnostics of anisotropic, vortex, exchange-biased magnetic structures, visualization of the micromagnetic structure of the surface layers of ferrite garnets, based both on the high sensitivity of the optical second harmonic generation method to the magnetic state of nanostructures and interfaces, and on the symmetry properties of high-order magnetization-induced susceptibility tensor have been demonstrated.

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Biophysics and medical physics

Quantifying the influence of the axial field of view, crystal material and object heterogeneities on the NEMA NU-2 scatter fraction estimation method: A Monte Carlo simulation study of the uEXPLORER PET scanner.

Quantifying the influence of the axial field of view, crystal material and object heterogeneities on the NEMA NU-2 scatter fraction estimation method: A Monte Carlo simulation study of the uEXPLORER PET scanner.

M. El Katib$^1$, E. Chakir$^1$, R. Sebihi$^2$, H. Saikouk$^{2,3}$

Moscow University Physics Bulletin 2024. N 2.

In Positron Emission Tomography (PET), the scattered photons represent a major image degrading factor. The scatter fraction (SF) of PET scanners is experimentally determined following the National Electrical Manufacturers Association (NEMA) NU 2 protocol, using a polyethylene phantom with a line source inserted at 45 mm radial offset from the phantom’s center. In this work, we aim to investigate the optimal radial offset of the line source, that represents the SF of a uniformly activated phantom, for the Lutetium Yttrium Orthosilicate (LYSO)-based uEXPLORER total body PET scanner. Additionally, we propose to study the impact of several factors (axial field-of-view (AFOV), crystal material and heterogeneities) on this optimal offset, in an effort to provide recommendations for a wide range of PET scanner configurations. We performed Monte Carlo (MC) simulations of the uEXPLORER scanner along with five phantoms of different diameters, using the Geant4 Application for Tomographic Emission (GATE) code. We performed supplemental MC simulations in which we varied the crystal material, the AFOV and we introduced bone and lung heterogeneities in the phantoms to asses their impact on the optimal offset findings. Our results demonstrated that the 45 mm offset overestimates the SF of the uniform 20 cm diameter phantom by 24.3%. Instead, an offset of 87 mm was reproducing this SF. For the phantoms having diameters in the range of 10-50 cm, an offset of 90.7% of the phantom’s radius was shown to be optimal (best fit). No AFOV-related impact has been observed on this optimal offset. The influence of the heterogeneities was also small with less than 1.1% absolute deviation in the SF. This offset could then be used for all AFOV lengths PET scanners using LYSO crystal. The impact of the crystal material was shown to be minimal and an offset of 91.5% of the phantom’s radius is consequently recommended as an average for other PET scanners.

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Physics of nuclei and elementary particles

PMAXS Library Generation for the Benchmark on Rostov-2 VVER-1000 Reactor

PMAXS Library Generation for the Benchmark on Rostov-2 VVER-1000 Reactor

M. Kheradmand Saadi

Moscow University Physics Bulletin 2024. N 2.

Recently, the OECD/NEA organization developed a benchmark problem based on a specific experiment conducted during the Rostov-2 first start-up procedure. The first phase of this benchmark gives an option to participants to develop their own two-group, assembly-wise homogenized cross sections. The main objective of this research is description of different techniques and methods employed during our own PMAXS libraries generation as well as their verification. The sophisticated SERPENT-2 Monte Carlo code has been employed for neutron transport in five distinct types of fuel assemblies and their corresponding group constants generation in a burnup and branch hierarchical structure. For each assembly 7 burnup states, 3 fuel temperature points, 2 moderator temperature points, 2 boron concentrations and 2 control rod states have been considered. The output files have been converted to PMAXS format using GENPMAXS interface. The verification of generated libraries has been conducted with two independent approaches. The first one is based on the comparison in assembly multiplication factor resulted from SERPENT and GENPMAXS codes. The results showed that the maximum reactivity difference between two codes is only 29 pcm. In second approach, the generated libraries have been fed to the PARCS code and neutronic results compared with reference data. The results showed that at different burnup states, the radial relative power and burnup distributions resulted from PARCS calculations are in good agreement with corresponding reference values. The maximum relative difference was less than %4 and the location of “hot assembly” was same.

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Investigation of $1^-_1$ excited states of even-even nuclei

Investigation of $1^-_1$ excited states of even-even nuclei

R. V. Jolos, E. A. Kolganova

Moscow University Physics Bulletin 2024. N 2.

General information on the structure and properties of the first excited $1^-$ states of even-even nuclei is given. Poorly-studied characteristics of $1^-$ states which are of interest for study within the framework of the research program at the Compton source of monochromatic gamma rays of ICPM INOC are discussed.

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Electric dipole polarizability of magic nuclei

Electric dipole polarizability of magic nuclei

N. N. Arsenyev, A. P. Severyukhin

Moscow University Physics Bulletin 2024. N 2.

The correlations between the electric dipole polarizability and neutron skin thickness are studied by the magic nuclei~$^{40,48}$Ca, $^{68,78}$Ni, $^{132}$Sn, and $^{208}$Pb. The strength distribution of the $E1$~transitions is calculated within the random phase approximation model based on the Skyrme nuclear energy density functional. A comparison with the experimental data has allowed us to constrain the value of the nuclear symmetry energy $J=30-37$~MeV.

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The laser-electron source of X-ray radiation (from the opening statement at workshop dedicated to the 85th anniversary of B.S. Ishkhanov in SINP MSU on October 26, 2023)

The laser-electron source of X-ray radiation (from the opening statement at workshop dedicated to the 85th anniversary of B.S. Ishkhanov in SINP MSU on October 26, 2023)

I. A. Artyukov$^1$, A. V. Vinogradov$^1$, V. I. Shvedunov$^{1,2}$

Moscow University Physics Bulletin 2024. N 2.

The work, as well as the seminar at which it was reported, is devoted to the memory of the outstanding physicist-nuclear scientist, professor of Moscow State University B.S. Ishkhanov, namely his contribution to the research and development of LEXG - laser-electronic X-ray generators. Relevance and prospects of this direction are connected with «gap» between two existing types of X-ray sources: on the one hand - X-ray tubes, and on the other - electronic accelerators, storage rings and free electrons lasers. It’s about a huge difference in their bundle characteristics, cost, scale, energy consumption, etc. The history of modern projects abroad, as well as the LEXG project of MSU - Jilin University, led by Prof. B.S. Ishkhanov, are briefly presented. From the point of view of their applications, the LEXG designs can be divided into two types with different scale of the devices. The first is the use of serial X-ray tubes and the second is radiation medicine, nuclear technology and nuclear physics research. International conferences on LEXG have been held since 2008. The list of these is given in the Annex to the article.

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X-ray lensless optics and ptychography

X-ray lensless optics and ptychography

A. S. Busarov$^1$, P. Yu. Glagolev$^2$, N. L. Popov$^1$

Moscow University Physics Bulletin 2024. N 2.

One of the tasks of modern optical methods is the most complete description of the objects and light fields under study. For example, the materials under study must be characterized not only by absorption, but also by refraction, and the light fields behind the object and near the detector - not only by intensity, but also by phase. The 1972 work of Gershberg and Saxton was the first attempt to accomplish this task without using any optical elements, relying only on a quadratic detector and a computer simulating the propagation of electromagnetic waves. Today, such lensless imaging methods are used in a wide range of wavelengths, from terahertz to hard x-rays. The purpose of this work is to give a brief introduction to the theory of lensless methods as applied to the X-ray wavelength range. The results of experiments on lensless imaging of test objects, recently performed at the Lebedev Physical Institute using lasers, are also presented.

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Theoretical and mathematical physics

A new microscopic representation of the spin dynamics in quantum systems with biquadratic exchange interactions

A new microscopic representation of the spin dynamics in quantum systems with biquadratic exchange interactions

M. I. Trukhanova$^{1,2}$, P. A. Andreev$^1$

Moscow University Physics Bulletin 2024. N 2.

There is a version of the Landau-Lifshitz equation that takes into account the Coulomb exchange interactions between atoms, expressed by the term $\sim\bm{s}\times\triangle\bm{s}$. On the other hand, ions in the magnetic materials have several valence electrons on the $d$-shell, and therefore the Hamiltonian of many-electron atoms with spins $S>1$ should include a biquadratic exchange interaction. We first propose a new fundamental microscopic derivation of the spin density evolution equation with an explicit form of biquadratic exchange interaction using the method of many-particle quantum hydrodynamics. The equation for the evolution of the spin density is obtained from the many-particle Schrodinger-Pauli equation and contains the contributions of the usual Coulomb exchange interaction and the biquadratic exchange. Furthermore, the derived biquadratic exchange torque in the spin density evolution equation is proportional to the nematic tensor for the medium of atoms with spin $\textit{S = 1}$. Our method may be very attractive for further studies of the magnetoelectric effect in multiferroics.

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Two-dimensional transient contrasting structure evolution in an inhomogeneous media with the advection

Two-dimensional transient contrasting structure evolution in an inhomogeneous media with the advection

B. A. Alexey

Moscow University Physics Bulletin 2024. N 2.

The inner transition layer evolution for two-dimensional quasi-linear initial-boundary value problem for the reaction-advection-diffusion equation in an inhomogeneous media with a small parameter within the high order derivatives is considered. Within the framework of the main (zero order) sum of the asymptotic series, the position of the inner transition layer is described by the Hamilton-Jacobi equation. The potential is calculated as an integrated density function of the reaction sources within the limits of the equilibrium levels. The front line of the transition layer evolves in the same way as the constant-eikonal line (the wavefront line in the other words) for the problem of wave propagation in an inhomogeneous medium in short-wave (geometro-optical) asymptotics. The sum of the asymptotic series of zero order and first order is found, the existence gap of a smooth front line, the time of destruction of the contrasting structure are calculated.

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Phase transition face-centered cubic crystal – homogeneous phase in helium

Phase transition face-centered cubic crystal – homogeneous phase in helium

P. N. Nikolaev

Moscow University Physics Bulletin 2024. N 2.

In this work, the characteristics of the phase transition face-centered cubic crystal - homogeneous phase in helium are calculated based on the correlation cell-cluster expansion. The theoretical data were compared with experimental data and good agreement was obtained. It is discussed the use of data on phase transitions in helium to estimate thermodynamic characteristics phase transition in a quantum system of hard spheres.

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Constancy of stabilized Randall-Sundrum model with respect to quantum corrections

Constancy of stabilized Randall-Sundrum model with respect to quantum corrections

I. P. Volobuev, S. I. Keizerov, E. R. Rakhmetov

Moscow University Physics Bulletin 2024. N 2.

In the Randall-Sundrum model stabilized with the help of the Goldberger-Wise scalar field, the lowest order vacuum quantum corrections to the energy-momentum tensor of the scalar and tensor fields are calculated. It is shown that the corresponding vacuum energy density of the fields in the bulk leads to the Casimir effect. Using the dimensional regularization method and the Abel-Plana formula, the divergences have been isolated and the vacuum energy density has been renormalized. An analytical expression for the Casimir force is obtained and an estimate of its influence on the model parameters is made. It was found that the quantum corrections lead only to a negligibly small decrease in the distance between the branes, i.e. the model possesses constancy with respect to quantum corrections.

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Limit flames combustion products stability in vertical tubes

Limit flames combustion products stability in vertical tubes

I. A. Gulyaev$^1$, K. A. Kazakov$^2$

Moscow University Physics Bulletin 2024. N 2.

Stability of the gas flows generated by steady near-limit flames propagating in vertical tubes is studied numerically. Basic scenarios of the burnt gas flow evolution are identified in relation to the thermal gas expansion parameter and the normal flame speed. It is shown that the realization of specific scenario essentially depends on the stagnation zone width as well as on the distance travelled by the gas from the flame front to the tube end. In particular, it is found that for sufficiently short distances, the burnt gas flows are stable provided that the stagnation zone width is less than half the tube diameter. Otherwise, an unstable flow evolution can lead to the appearance of recirculation domains and acoustic perturbations.

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Optics and spectroscopy. Laser physics

Assessment of dynamic disorder in DNA oligonucleotides using low-frequency Raman spectroscopy

Assessment of dynamic disorder in DNA oligonucleotides using low-frequency Raman spectroscopy

A. Yu. Sosorev$^{1,2,3}$, O. D. Parashchuk$^1$, A. A. Trubitsyn$^1$, N. O. Dubinets$^{2,4}$, I. V. Chicherin$^1$, D. Yu. Parashuk$^{1,2}$

Moscow University Physics Bulletin 2024. N 2.

The degree of DNA compaction in various regions of the cell nucleus determines whether the corresponding genes should be expressed, and whether other important cellular processes, such as DNA replication and repair, should take place. However, approaches to the experimental assessment of the compactness of DNA in cell nuclei, as well as its indicator, dynamic disorder — thermal fluctuations in the position and mutual orientation of molecular fragments — are practically not developed. In this paper, using single-stranded oligonucleotides guanine and cytosine, as well as their double-stranded combination as an example, we show that dynamic disorder in DNA can be estimated using low-frequency Raman spectroscopy. For the first time, the Raman spectra of oligonucleotides were measured in a wide range including the low-frequency and high-frequency regions. It was found that the low-frequency Raman intensity is maximal for single-stranded oligocytosine and minimal in double-stranded oligonucleotide, in full agreement with the magnitude of dynamic disorder estimated from the molecular dynamics simulations. The results obtained indicate the prospects of using low-frequency Raman spectroscopy to assess the dynamic disorder and compactness of DNA. It is expected that the use of such a technique should contribute to the understanding of key cellular processes and their underlying physical mechanisms, which is necessary for the development of advanced methods of molecular biophysics and cell biology.

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Condensed matter physics

Field emission from point diamond cathodes under continuous laser irradiation

Field emission from point diamond cathodes under continuous laser irradiation

V. I. Kleshch, I. R. Anderzhanov, R. R. Ismagilov, A. N. Obraztsov

Moscow University Physics Bulletin 2024. N 2.

The presented study investigates the impact of continuous laser irradiation in the visible range on the field emission properties of diamond needle-like micro-sized crystallites with a nanometer tip radius. The measurements were carried out in a vacuum diode configuration with a flat metal anode using DC voltage source. It was found that the field emission current increased under illumination, showing a direct correlation with the radiation power. The relative increase in current under the action of laser irradiation is determined by the parameters of the dark current-voltage characteristic and reaches its maximum value in the region corresponding to the minimum increase in dark current with voltage. It is shown that the most likely mechanism for the increase in current is a change in the electrical resistance of the diamond microneedle as a result of absorption of laser radiation in the presence of electron levels located in the band gap of the diamond associated with impurities or structural defects in the near surface layer of the diamond microneedle.

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Calculation of the effective mass of electrons and holes of a single crystal TlGaTe2

Calculation of the effective mass of electrons and holes of a single crystal TlGaTe2

A. P. Abdullayev, D. M. GAFAROVA

Moscow University Physics Bulletin 2024. N 2.

Based on the band structure of the compound, the extrema of the valence and conduction bands were determined and the tensor of the components of the inverse effective mass of electrons and holes was calculated.

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Astronomy, astrophysics, and cosmology

Simulation of emission of the flare 27.04.2012 in spectral lines of Hydrogen, Helium and Calcium

Simulation of emission of the flare 27.04.2012 in spectral lines of Hydrogen, Helium and Calcium

Yu. A. Kupryakov$^1$, K. V. Bychkov$^2$, O. M. Belova$^4$, V. A. Maliytin$^5$, A. B. Gorshkov$^3$

Moscow University Physics Bulletin 2024. N 2.

Тhe article is devoted to analyses of solar flare SOL2012-04-27 emission in Hydrogen, Helium and Calcium spectral lines observed on horizontal solar equipment HSFA-2 in Ond\u{r}ejov observatory. The integrated fluxes are calculated. The data collected are treated in the approach of the fast energy release followed by gas evaporation. The gas parameters are calculated with chromosphere conditions and spectral line self-absorption taken into account. Encompassing of six lines allows to reveal the temperature, density and extent of the gas with high degree of validity. The best agreement of the theory with observations is obtained in the model of the spread of inhomogeneous clouds, each of which has hot ($T\approx18000\div19500$~K) and cool regions ($T\approx8000\div9000$~K). On average, one cloud gives about ten percent of the total flux.

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Physics of Earth, atmosphere, and hydrosphere

Effects of wind on deep convection in Lake Baikal during the autumnal thermal bar

Effects of wind on deep convection in Lake Baikal during the autumnal thermal bar

B. O. Tsydenov, N. S. Trunov, V. V. Churuksaeva, D. V. Degi

Moscow University Physics Bulletin 2024. N 2.

The results of numerical modeling of processes of deep convection in Lake Baikal during the autumnal thermal bar are presented. Analysis of the space---time distributions of temperature under different wind conditions was conducted on an example of the Boldakov River---Maloye More Strait cross-section which is characterised by the great depths. Simulations have shown the effectiveness of wind only in the upper 250 m layers. However, cabbeling instability generated by the thermal bar can lead to convective mixing to a depth of ~600 m.

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Engineering physics

Beam Scanning System for an Industrial Electron Accelerator

Beam Scanning System for an Industrial Electron Accelerator

M. A. Borisov, V. I. Shvedunov

Moscow University Physics Bulletin 2024. N 2.

To create a compact system for scanning the beam along the conveyor, this paper considers the horizontal placement of the accelerator with a magnetic system with rotating the beam by 90 deg. A three-dimensional simulation of the magnetic system and the dynamics of electrons in it was performed. Dose distributions were also obtained in the near-surface region of the irradiated object, on the basis of which the optimal laws of change in the current and voltage of the scanning magnet were determined, which provide the required conditions for irradiating the product.

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