Physics of Atomic Nuclei最新文献

At NRNU MEPhI, the world’s largest coordinate detector TREK is being created using drift chambers to study cosmic ray muons. The basis of the installation is multiwire drift chambers (DC), previously used in the neutrino detector at the Institute of High Energy Physics (Protvino, Moscow oblast) at the U-70 accelerator. To study the characteristics of DCs before installation in the TREK and the projected MDM detector, a stand was created that makes it possible to determine their efficiency, coordinate and angular accuracy, and zone characteristics. The article presents the design of the stand and the results of testing 394 DCs for the TREK and MDM installations.

The Proryv project is developing effective ways of reprocessing irradiated nuclear fuel (SNF) to return long- lived radionuclides to the fuel cycle and close it. One of the challenges of closed fuel cycle development is the reprocessing of highly active nitric acid raffinates from the PUREX process. To do so, americium-241 must be separated from liquid radioactive waste. Technologies for the extraction, sorption, purification, and concentrating of radionuclides are widely used when processing and fractionating liquid radioactive waste. The highest efficiency and selectivity in the extraction of actinoids (III) and lanthanides (III) with rare earth elements (REE) and transplutonium elements (TPE) from nitric acid solutions of spent nuclear material reprocessing are shown by extractants based on N, N, N', N'-tetraoctyldiglycolamide (TODGA). Before using a solid-phase extractant based on TODGA, ions of the substance in the solution must be converted to neutral complexes or other nondissociated compounds. This can be done by adding neutral salts to the solution that reduce the solubility of the elements to be separated, shift the distribution of extraction, and greatly improve the efficiency of extraction. The extracted substance is taken in the form of a new phase: a solid precipitate, or a liquid or a gas phase. (With liquid extraction, there is an increase in the capacity of the extractant for the target component). Adding salts or salting agents to an aqueous phase to improve the ionic strength of a solution raises the coefficients of distribution of extracted substances, which in turn increases the capacity of sorbents. The aim of this work is to study the salting out of americium-241 during sorption using an experimental modified sample of solid-phase extractant based on TODGA and model solutions of liquid radioactive waste with a uranium macrocomponent for different contents of NaNO₃. It is found that the highest coefficients of distribution for the sorption of americium-241 and uranium are obtained in a solution containing 100 gL of NaNO₃, but this effect is much less pronounced for uranium than for americium-241. Studying the sorption kinetics of americium-241 and uranium reveals the salting effect, which is confirmed by the equilibrium concentrations of americium-241 and uranium in the solution at the same time but with different concentrations of NaNO₃. The difference between the equilibrium concentrations for americium-241 is an order of magnitude, in favor of a drop when the concentration of NaNO₃ is raised to 100 gL. The use of this effect allows the maximum capacity for americium-241 to be obtained in a system with uranium macrocomponents.

The potential of utilizing a multiple cell array detector (MCAD) [8] has been demonstrated as an additional tool for correlation studies of density and poloidal field fluctuations in a plasma as a part of the heavy ion beam probe on the T-15MD tokamak. The optimum position and size of the MCAD have been found, and its cell size has been determined. Trajectories of probing particles have been calculated and the plasma region for measurements has been estimated for the toroidal magnetic fields B_T = 1.2, 1.5, 1.7, and 2.0 T. It has been shown that simultaneous measurements with the MCAD and the energy analyzer as the main measurement tool are possible, which allows the study of radial and poloidal spatial correlations of medium scale comparable to the small plasma radius. The spatial resolution of measurements and attenuation of the beam current signal during its passage through the plasma have been estimated.

Samples of tin oxide nanoparticles were synthesized in a plasma discharge under the effect of ultrasonic cavitation. Using solution technology and then melt compounding technology, samples of polymer composite materials with a homogeneous distribution of nanoparticles were obtained. A copolymer of ethylene and vinyl acetate was used as a polymer matrix. Tin oxide nanoparticles in the form of an aqueous suspension synthesized in a plasma discharge under the effect of ultrasound were studied by dynamic light scattering, and it was shown that the synthesized particles have a distribution peak in the size range of 50–60 nm; under ultrasonic treatment, the distribution peak shifts to the region of 30–40 nm. Measuring the electrokinetic potential of the surface of the initial nanoparticles in an aqueous dispersion medium made it possible to establish that, under the effect of ultrasound, tin oxide particles acquire additional active adsorption sites capable of interacting with the functional groups of the polymer matrix. In images of composite material films obtained on a scanning electron microscope, nanoparticles and agglomerates of tin oxide nanoparticles are visible. According to X-ray diffraction and X-ray fluorescence analysis, it was possible to qualitatively confirm the presence of tin inside the polymer film: peaks related to tin oxide nanoparticles are visible in the spectra.

The dependence of the focal length of the thallium Tl⁺ ion beam on the parameters of the ion-optical system of the injector for diagnostics of plasma by heavy ion beam probe has been studied. The possibility of obtaining quasi-parallel beams and converging beams with a focal length of more than 4 m has been shown. Experimental results are compared with the results of computer modeling of the beam trajectory in the injector.

The technology of lanthanum doping of oxidation-resistant Mo–Zr–Si–B coatings has been developed by using a 95% (90% MoSi₂ + 10% MoB) + 5% ZrB₂ target with LaB₆ segments for magnetron sputtering. A change in the current–voltage characteristic has been determined when using additional segments. It has been found that the use of LaB₆ leads to a decrease in the breakdown voltage of the glow discharge. Mo–Zr–Si–B and Mo–La–Zr–Si–B coatings with a uniform distribution of elements through the thickness, low roughness, and a low-defect structure have been obtained by magnetron sputtering. The use of LaB₆ segments during sputtering leads to amorphization of coatings and increased oxidation resistance under annealing in air at 1500°С.

This work considers planar channeling of relativistic particles in a comoving frame of reference moving at a speed equal to the longitudinal component of the velocity of the channeled particle. In SSO, the motion of a particle during planar channeling will be one dimensional, and for electrons and positrons with energies up to several gigaelectron volt, it will be nonrelativistic, as in the hydrogen atom. potential from transverse coordinates. To determine the main characteristics of such a movement, it is proposed to use approximate Bohr–Sommerfeld quantization methods, which make it possible to make such a calculation analytically. The approximate method for calculating quantum states can be extended to consider transverse motion beyond the nonrelativistic approximation, even in a comoving frame. The energy distributions of permissible states of transverse finite motion are found for several variants of model potentials. It is shown that, despite the difference in the structure of energy levels, the average distances between energy levels are practically insensitive to the choice of model potential. The energies of the transverse motion levels are found for the case where the nonrelativistic approximation is not applicable even in the comoving reference frame.

The effect of high-fluence 30 keV helium ion irradiation with the fluence from 10¹⁸ to 3 × 10¹⁸ cm^–2 in the temperature range from room temperature to 600°C on the morphology and surface structure of highly oriented pyrolytic graphite UPV-1T and fine-grained polycrystalline graphite MPG-8 has been studied experimentally. Ion-induced morphological elements complementing those previously established at low irradiation fluences (~10¹⁷ cm^–2) have been identified. Irradiation of highly oriented pyrolytic graphite at high fluences results in delaminations, which manifest themselves as graphite flakes that are bent, twisted, and have whisker-like structures. Irradiation of fine-grained graphite does not significantly change its microstructure compared to highly oriented pyrolytic graphite.

A comprehensive approach is being developed to monitor the leak tightness of fuel rod claddings in VVER nuclear reactors. One of the main stages is the reliable registration of the presence of a leaking fuel rod or rods in the core of the reactor during the operation of the power unit at full capacity. This paper discusses general trends in the changes in the activities of radionuclides resulting from fission in the coolant of the primary circuit of VVER nuclear reactors of various generations and designs. The experience of the Novovoronezh Nuclear Power Plant in the method of sampling and isolating inert radioactive gases from the primary circuit coolant is examined. A comparison of methods for measuring inert radioactive gases in the primary circuit coolant is conducted, including direct spectrometry, cryogenic methods, and vacuum extraction methods. The issue of reliably recording the time of fuel rod cladding breach during the operation of the reactor installation at full power is addressed, using the example of power unit no. 5 of the Novovoronezh Nuclear Power Plant. Comparative results of the analysis of the state of the reactor core regarding the leak tightness of fuel rods are presented, based on key reference radionuclides. The most reliable results that indicate a fuel rod breach were obtained from monitoring specific activities and analyzing the changes in the ratios of inert radioactive gases, performed using the vacuum extraction method for inert radioactive gases. Monitoring the specific activity of inert radioactive gases in the primary circuit coolant allows a highly accurate assessment of the condition of physical barriers. The proposed method for extraction and isolation of inert radioactive gases demonstrates high reliability and consistency of results, as an additional tool for monitoring the leak tightness of fuel rod claddings during the operation of a power unit at full capacity. With representative data on the specific activities of inert radioactive gases, one can reliably assess the condition of the fuel rods in the reactor core.

The probability P_NEET of excitation in the plasma of nuclei of multiply charged ions due to transitions in their electronic shells is considered, when the energy difference between nuclear and electronic transitions ΔE_NEET becomes small due to the deformation of the electron shells of ions during their collisions. It is shown that such a resonance is possible only in a two-component plasma containing, along with multiply charged ions, singly charged ions. For ΔE_NEET up to ~100 eV, the occurrence of resonance can increase the probability P_NEET by several orders of magnitude. It is noted that in plasma there is also the possibility of resonant conversion of the excitation of nuclei into the excitation of their electron shells.