Faculty of Physics
M.V. Lomonosov Moscow State University

# Issue 1, 2021

Biophysics and medical physics

## The restoration of a 4D image degraded by the limited spatial resolution of the PET system

### A. Bardane$^1$, J. Tajmouati$^1$, A. Maghnouj$^1$

Moscow University Physics Bulletin 2021. N 1.

The reconstruction of dynamic tomographic images is a demanding procedure in the diagnostic stage. In this study, we sought to develop an alternative approach to correcting partial volumes by reconciling on the integration of deconvolution in the iterative reconstruction of an image of 4D acquisitions (PET+time).

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## Influence of ionizing radiation on growth phytopathogen R. Solani

### U. A. Bliznyuk$^1$, V. A. Leontyev$^1$, A. A. Malyuga$^2$, V. V. Khankin$^3$, A. P. Chernyeav$^{1,3}$, N. S. Chulikova$^2$, D. S. Yurov$^3$

Moscow University Physics Bulletin 2021. N 1.

The study focuses on the development of the phytopathogenic fungus Rhizoctonia solani Kuhn grown from sclerotium, irradiated with 1 MeV electrons. Irradiation doses ranged from 20 Gy to 40 kGy with the average beam power of 25 kW. The growth of phytopathogen showed the nonlinear dependence on the dose during 96 hours of monitoring. The doses had both inhibitory and stimulating effects on R. solani. Doses 40 Gy and 600 Gy stimulated the growth of R. solani 1.1-1.2 times compared to the control samples. The samples irradiated with 75 Gy, 150 Gy and 900 Gy practically didn't differ from the control samples. However, the dose 1.8 kGy led to a significant slowdown in the development of the fungus during the first 48 hours of observation. Absorbed dose values exceeding 4.5 kGy completely suppressed germination of R. solani sclerotium.

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Physics of nuclei and elementary particles

## Monte Carlo simulation of a 18 MV medical linac photon beam using GATE/GEANT4

### M. Fiak, A. Fathi, J. Inchaouh, A. Khouaja, A. Benider, M. Karim, N. Harakat, Z. Housni, M. Bouhssa, M. Mouadil, Y. Elabssaoui, O. Jdair

Moscow University Physics Bulletin 2021. N 1.

In radiotherapy applications, Monte Carlo (MC) simulation for dose calculations is well acknowledged for its accuracy in predicting dose deposition in the patient. The full modeling of a high-energy photon beam from Varian Clinac 2100C 18 MV medical linear accelerator is presented here by using the GATE/GEANT4 Monte Carlo codes. To evaluate dose distributions associated with the simulated linac head model, dosimetric quantities including the Percentage Depth Dose (PDD), transverse dose profiles, and a set of beam-quality indicators were measured and calculated in a water phantom for square field sizes of 4x4 cm 2 and 10x10 cm 2 . Simulations accuracy was validated through Gamma Index analysis using different acceptance criteria within 2%/2mm, 3%/2mm, 2%/3mm, and 3%/3mm. In terms of Gamma Index comparison, good agreements were found between the calculated and measured dose distributions for all field sizes. The differences between simulation and measurement of beam quality indicators were smaller than 2%.

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## A simple method for evaluating the nucleon densities of atomic nuclei based on the microscopic charge densities

### M. V. Chushnyakova$^1$, I. I. Gontchar$^2$, O. M. Sukhareva$^1$

Moscow University Physics Bulletin 2021. N 1.

The nuclear fusion process represents an interesting example of collective nuclear motion. This process provides us with information on the interaction of nuclei and their structure. The theoretical analysis of the fusion cross-sections is often based on the double folding model which is used for calculating the potential energy of the interaction between the colliding nuclei (the nucleus-nucleus potential). The nucleon density is an important ingredient of this model. Evaluating these densities within the framework of the microscopic models is extremely complicated. In the present work, we propose a simplified way of calculating the proton and neutron densities based on the microscopic densities of six reference nuclei. The proposed approach enables us to obtain the nucleon densities spending minimal computer resources and can be easily used by experimentalists.

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## Influence of the statistical model parameters selection on r-process yields of the 180÷190Tb

### V. V. Negrebetskiy$^1$, K. A. Stopani$^2$

Moscow University Physics Bulletin 2021. N 1.

Theoretical cross sections of neutron capture reactions on the neutron-rich isotopes 180÷190Tb were obtained using the TALYS statistical model with various methods of calculating nuclear masses and energy level densities. Based on these data, reaction rates at a temperature of 1.2 GK, corresponding to the situation of explosive stellar evolution, were calculated. The obtained rates were used to simulate astrophysical r-process using the SkyNet nuclear reaction network library. Concentration deviations of r-process products, caused by statistical model parameters selection, were evaluated.

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Theoretical and mathematical physics

## Investigation of the applicability of the method for measuring the RCS of extended bodies based on the expansion of the near-field in terms of Slepian's functions by mathematical modeling

### N. P. Balabukha$^1$, D. A. Konyaev$^{1,2}$, N. E. Shapkina$^{1,2}$, K. M. Shitikova$^2$

Moscow University Physics Bulletin 2021. N 1.

Methods for measuring bistatic RCS of objects using near-field scanning and near-field to far-field transformation by mathematical modeling are analyzed. A model two-dimensional problem of diffraction by extended scatterers is considered. A cylindrical scanner is used. An important issue in this case is the possibility of scanning not on the full scanning surface, but on a truncated one in order to to reduce the cost of measurements. Under such conditions the results of the classical method become poorly predictable, and an adapted method is required. Two methods based on the expansion in cylindrical waves in the case of scanning on a truncated surface are compared: The classical one, used to measure antenna radiation patterns (the field outside the scanning area is assumed to be zero) [1] and the method proposed by K. T. Kim, which allows to take strictly into account the truncation of the scanning surface by angle [2]. Comparison of the obtained results of both methods confirms the prospects of using the second method.

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## Conductivity in composite materials based on oriented carbon nanotubes

### E. A. Vorobyeva$^{1,3}$, A. P. Evseev$^{1,2}$, V. L. Petrov$^1$, A. A. Shemukhin$^1$, N. G. Chechenin$^1$

Moscow University Physics Bulletin 2021. N 1.

The article discusses the prospects of using composite materials based on polymer matrices with the inclusion of carbon nanotubes, including oriented ones, as both functional and structural materials for nanosatellites. An assessment of the thermal conductivity and electrical conductivity of these composites is presented, and methods are proposed for obtaining carbon nanotubes, including vertically alligned ones synthesized on filaments, as well as axially regular nano-mesostructures, as a functional additive for varying the properties of materials.

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Optics and spectroscopy. Laser physics

## On the choice of a strategy for broadband optical monitoring of the deposition of multilayer coatings

### T. F. Isaev$^1$, A. V. Tikhonravov$^2$, A. G. Yagola$^1$

Moscow University Physics Bulletin 2021. N 1.

The correlation of errors for various broadband optical monitoring strategies for controlling deposition of multilayer coatings, including strategies with replaceable monitoring chips, is investigated. It is shown that it is necessary to take into account the effect of error self-compensation when choosing a monitoring strategy. The results of this study can be used to select the most promising monitoring strategy for a given type of multilayer coatings.

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Condensed matter physics

## Magnons and edge modes in chains of non-spherical magnetic particles

### A. M. Pikalov$^{1,2}$, A. V. Dorofeenko$^3$

Moscow University Physics Bulletin 2021. N 1.

Spin waves in chains of magnetic particles of elliptic shape magnetized along the chain axes are studied. Dispersion relations are found, boundaries of the transmittance band are derived analytically. It is shown that edge modes arise at the chain ends, and their existence is due to static scattering fields which attenuate near the ends of the chain.

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Chemical physics, physical kinetics, and plasma physics

## The simulation of a shock wave impact on the electron temperature of the argon plasma discharge positive column

### A. K. Sukhov

Moscow University Physics Bulletin 2021. N 1.

A computer simulation of shock wave impact on the plasma electron temperature of discharge positive column in argon was performed. A one-dimensional hydrodynamic model of gas discharge plasma is used, supplemented by a formula for the relationship of the relative electron temperature with the reduced electric field strength. The distribution of the electron temperature in the shock wave is obtained, and the influence of its intensity is estimated. The simulation results are compared with experimental data.

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