Faculty of Physics
M.V.Lomonosov Moscow State University
Physics of nuclei and elementary particles

Empirical estimate of np-pairing magnitude in N=Z nuclei

B. S. Ishkhanov$^{1,2}$, S. V. Sidorov$^1$, T. Yu. Tretyakova$^2$

Memoirs of the Faculty of Physics 2018. N 1.

In studies of neutron-proton pairing the empirical evaluations based on nuclear masses are of particular importance. In the current work, various mass relations are analysed by the example of N=Z nuclei and essentially different formulas used for estimation of np-pairing energy in self-conjugate nuclei are shown to yield similar results. Correlations between the obtained values and the spectra of isobaric analogous states indicate that mass relations may be used to describe the isovector (T=1) component of np-pairing to sufficient accuracy, providing however little or no information regarding the isoscalar component T=0.

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Influence of the energy spectrum of an electron beam on the estimation of its energy by the method of attenuation of bremsstrahlung by an absorbing barrier

L. Yu. Ovchinnikova$^{1,2}$, V. I. Shvedunov$^{1,2}$

Memoirs of the Faculty of Physics 2018. N 1.

The procedure for measuring the energy of a nonmonochromatic electron beam by the method of attenuating bremsstrahlung by an absorbing barrier is simulated using the analytical expression for the bremsstrahlung spectrum. The energy value measured by this method is compared with the mean energy and energy of the maximum of the electron beam spectrum. It is shown that the energy estimate obtained by the attenuation barrier method depends on the form of the electrons energy spectrum and is closer to the average energy than to the energy of the maximum of the spectrum, which, as a rule, is the main optimized parameter in calculating beam dynamics in the accelerator.

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Chemical physics, physical kinetics, and plasma physics

Analysis of characteristics of the magnetotail current sheet during geomagnetic perturbations

V. I. Djmrin$^1$, H. V. Malova$^2$, V. Yu. Popov$^1$

Memoirs of the Faculty of Physics 2018. N 1.

On the base of numerical simulation the evolution of current sheet (CS) in the Earth’s magnetotail during geomagnetic perturbations is investigated. The evolution of the pressure tensor in the process of CS thinning to extremely thin configuration playing a key role in large-scale geomagnetic perturbations is considered. It is shown in a frame of numerical experiment that at an early stage the CS is formed with thickness about 8-10 Larmor proton radii and gyrotropic pressure distribution. This stage is characterized by plasma drift motion to CS center and to the Earth, and can be well described by the Chew-Goldberger-Low approximation. At the later stage the extremely thin current sheet is formed in which plasma pressure tensor becomes anisotropic. Estimates of characteristic timescales of the system evolution are made and the agreement with the available experimental data is shown.

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Teaching methods

Practical work on physics as a whole scientific research based on open data

I. V. Kuznetsova$^1$, M. E. Prokhorov$^2$

Memoirs of the Faculty of Physics 2018. N 1.

The article describes a new model of practical work in physics on the basis of modern scientific data placed in the public domain. It assesses the frequency of asteroids falling to Earth by counting the number of craters on the Moon and discusses the various mechanisms of the formation of craters depending on the parameters. This work has several significant methodical benefits over traditional teaching labs. Firstly, the work is dedicated to the relevant scientific problem. Secondly, it forms in students an idea of the diverse relationships between studied objects and scientific methodology that takes into account some aspects of the phenomenon and discarded others. Third, the work has a multidisciplinary. It uses reference data from different branches of physics, geology and astronomy. Practical elaboration has a distinct visibility and it offers the possibility to vary the data materials used in the work. The proposed laboratory work is universal, does not require expensive equipment to carry it out, and can be used in distance education.

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Optics and spectroscopy. Laser physics

Laser-induced modification of aluminum micropowders in selective laser melting mode

F. V. Kashaev$^1$, D. V. Shuleiko$^1$, S. V. Zabotnov$^1$, A. V. Skobelkina$^1$, A. K. Petrov$^2$, A. V. Chetvertukhin$^3$, P. V. Evdokimov$^4$, A. V. Garshev$^4$, V. I. Putlayev$^4$

Memoirs of the Faculty of Physics 2018. N 1.

Selective laser melting of the powders of AlSi10Mg alloy, characterized various sizes and shapes of particles, has been carried out in vacuum and argon by laser pulses with submillisecond duration. As a result of this modification, the structures are formed with porosity, depending both on the geometric parameters of the particles in the initial powders and on the atmosphere in which irradiation was carried out. For the first time by means of the Raman spectroscopy a considerable change in the mechanical stresses and fraction of crystalline state silicon in the studied structures before and after selective laser melting was registered.

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