No 6 (2023)

An experimental facility has been developed by MEPhI to study the spectrometric characteristics of gas mixtures for cascade gas electron multipliers (GEMs), which are widely used in modern tracking, Cherenkov, and synchrotron-radiation detectors designed for high-energy physics experiments. The characteristics of the gas mixture for the GEMs used in the BM@N international experiment (Joint Institute for Nuclear Research, Dubna) have been investigated. The applicability of this facility for laboratory works accompanying the Nuclear Physics and Technology master’s courses is noted.

A packaged power detector made in a waveguide with a standard cross section of 2.4 × 1.2 mm2 for the three-millimeter wavelength range with good enough matching for this type of device is presented. The design uses low-barrier diodes made on the structure of domestic production. The calculated and experimental characteristics of the detectors are given, such as the frequency dependence of the sensitivity and the level of the standing wave ratio (SWR). It is shown that the average sensitivity of the detectors over the range is more than 1000 V/W, and the SWR value is no more than 3.

Plasma flows with high velocity, density, and energy are widely used in research on the interaction of plasma with materials, modeling of astrophysical processes, development of plasma thrusters and plasma radiation sources, and plasma injection into fusion devices. Electrodynamic plasma guns can be used to generate such flows. This paper describes the design features of a powerful pulsed plasma gun and diagnostic tools for measuring the parameters of the plasma flow generated by it.

Information about charged particles emitted by plasma of high-current discharges is of interest both from the point of view of understanding the fundamental processes occurring in pulsed plasma and for applied problems. Compact magnetic spectrometers based on permanent magnets make it possible to measure the flux of charged particles from a plasma under conditions of strong electromagnetic noise. Imaging plates (IP) are one of the most commonly used types of detectors for detecting charged particles in laser-plasma and electric-discharge experiments. This paper presents the results of calibration of the BAS-MS IP when detecting electrons and the BAS-TR IP when detecting helium and tungsten ions. Calibration dependences of the sensitivity of the BAS-MS IP for electrons in the energy range of 0.65–50 MeV and the sensitivity of the BAS-TR IP for tungsten ions in the energy range from 20 eV to 650 keV are obtained, taking into account the angles of incidence of particles on the detector.

The characteristics of the calibration beam of secondary electrons at the Pakhra accelerator based on the SP-3 magnet at the Lebedev Physical Institute are presented. The energy resolution of a beam with a 2-mm-thick copper converter in the electron energy range E = 5–100 MeV is δ ≈ 10%.

We describe a technique for online control of the reliability of the data of magnetic circular dichroism spectroscopy in reflected light, which is based on measuring the polar magneto-optical Kerr effect under normal incidence of light on a sample with a method of phase modulation of a light wave using a photoelastic modulator. The presented technique involves measuring the amplitudes of signals at the “zero” (V=) and doubled (V2f) frequency f of the retardation modulation in crossed polarizers in the process of scanning over a spectrum. In these measurements, the constancy of the V2f/V= ratio over the entire spectral range confirms the reliability of the spectroscopy data. The possible instrumental errors that lead to a distortion of the recorded spectrum shape were analyzed. The operability and efficiency of the technique is illustrated by an example of measuring the magnetic circular dichroism spectrum of a MnAs film.

The design and parameters of a compact excilamp with an original sealed-off emitter made of a quartz tube with an outer diameter of 21 mm are described. The characteristics of xenon radiation in the vacuum ultraviolet region of the spectrum have been studied. On the band of the second xenon continuum, which has a maximum at the wavelength λ ≈ 172 nm, at a pulse repetition rate of 96 kHz, a radiation power density of 30 mW/cm2 was obtained. The excilamp was used for excitation of polymethyl methacrylate, in which a photoluminescence band was recorded in the spectral region of 380–480 nm.

Theoretical and experimental studies of the magnetic field distribution in the space between two cylindrical permanent magnets with through holes in the center have been carried out. In the middle of a space measuring 2 × 2 × 2 mm3 near the symmetry axis, a magnetic field with an inhomogeneity of no more than 3% was found and one in the region of 1 × 1 × 1 mm3 with less than 1% was found. Based on the calculated and experimental results, a setup for determining the Verdet constant (V) using neodymium permanent magnets was developed and manufactured. The magneto-optical constants for samples of optical ceramics from Tb2O3 and Tb3Ga5O12 at wavelengths of 0.628 and 1.06 µm are determined.

One of the methods for obtaining 123I is the bombardment of gaseous 124Xe with protons, in which nuclear reactions of production and decay of 123Xe and 123I isotopes occur. After irradiation, the gas phase is condensed from the target into a special “decay container,” in which the target isotope 123I is produced and accumulated during 123Xe decay. The amount of 123I produced in the target and deposited on its walls during the irradiation is comparable to the amount of 123I obtained in the decay container. A laboratory setup has been created and a process technology for extracting 123I from the walls of the target has been developed to increase the total yield of 123I. Organic solvents (acetone and diethyl ether) are used for this purpose. The proportion of the 123I extracted by washing off from the walls of the aluminum target is at least 84%. The loss during subsequent vacuum distillation of solvents does not exceed 5%. After vacuum distillation, the extracted 123I is dissolved in NaOH. At this stage, the efficiency of 123I washing-off with a 0.01 M NaOH solution is at least 95%. Nevertheless, even taking into account these losses, the proposed method makes it possible to additionally extract the 123I radionuclide from the target in an amount equal to or greater than the activity of the 123I produced using the existing technology.

The paper considers various designs of detectors for the passage of charged microparticles, which can be installed on mass spectrometers in order to record the moment of passage of a microparticle and initiate the measurement process. The largest range of recorded masses and velocities was shown by the detector design, made on the basis of a dielectric base (PLA plastic) using a 3D printer and a nichrome filament.

A universal hardware complex for generating traditional low-temperature plasma and two types of nonthermal atmospheric pressure plasma is presented. The basis of the complex is a low-budget magnetron microwave generator used in microwave ovens for household and industrial purposes. In model experiments with cultures of microorganisms, the biocidal properties of the generated argon nonthermal plasma were confirmed. The sterilizing properties of plasma during the treatment of the surface of the seed material have been established.

An apparatus for studying the processes of laser action on various materials, including biological tissue, is described. The system makes it possible to obtain thermograms of the sample surface, conduct high-speed video recording, and record acoustic signals in a wide frequency range during experiments. The system was tested using a pulsed nanosecond high-frequency laser source with a wavelength of 3.03 μm. The samples were exposed to pulses with a duration of 1.5 ns and a frequency of 8 MHz. It is shown that it is possible to use a laser system to obtain incisions on biological tissues of various types without carbonization. The obtained experimental data made it possible to clarify the mechanism of the action of laser radiation on the surface of water-saturated biological tissues.

New possibilities for the mode of detecting backscattered electrons in a scanning electron microscope (SEM) are presented. The technique for determining the chemical composition of the probed area of the sample using the precalibrated scale of the SEM’s gray screen has been further developed. Simple relationships are presented for practical application in finding the thicknesses of thin films on a massive substrate. The parameters of the double layer of the film nanostructure on the substrate are determined, that is, depth and thickness of subsurface fragments of the microobject. A technique is proposed for measuring the surface potential of negatively charged dielectric samples upon irradiation with medium-energy electrons

A setup for determining the contact electrical resistance measured using two surface point potential probes installed at the same distance from the contact surface is described. The total number of paired probes located at different distances from the contact surface is four. The reference temperature range is 380–1500 K. Measurements can be performed in vacuum and in air. The setup allows one to investigate the contact resistance at a direct current, which may vary from 20 to 120 A. The first test experiments have shown that changing the current polarity does not affect the current–voltage characteristic measured on a monolithic sample or on a sample with one fixed contact surface.

An experimental setup for studying pulse gas flows within short periods (up to 1 ms) was developed and an experimental data processing method is presented. Based on high-speed frame interferometry data and the results of dynamic pressure measurements, the spatial and temporal distributions of the helium flow density and velocity are determined. The optimal method for reconstructing the spatial density distributions with consideration for the experimental errors is described. The presented method allows characterization of the gas flows with a density of more than 0.0001 kg/m3 and a velocity of more than 400 m/s.

The design of the portable Wilson cloud chamber and devices included in it are described. The main performance characteristics of these devices are presented. Multiple tests of the setup have been carried out, and the main parameters of its functioning, as well as the required parameters of the cooling system, have been determined. This Wilson cloud chamber is used as the scientific, laboratory, and demonstration equipment.

Detector of vavilov–cherencov radiation 
initiated by wide atmospheric showers of cosmic rays