BULLETIN OF THE L.N. GUMILYOV EURASIAN NATIONAL UNIVERSITY. PHYSICS. ASTRONOMY SERIES

Optimization of the injection dose of PET/CT 18F‑FDG for nuclear medicine in Kazakhstan based on the national diagnostic reference levels of 2024.

2024-11-21T10:51:29+00:00

The use of 18F-2-fluoro-2-deoxy-D-glucose (18 F-FDG) (PET/CT) is useful for the functional diagnosis of neoplastic lesions, determining the stage of cancer and detecting metastases. Recently, it has become increasingly important to monitor effective radiation exposure to the patient without compromising image quality due to an increase in the number of PET/CT procedures. Modern medical radiation technologies, including the use of radiopharmaceuticals, are widely used today. It should be noted that these technologies themselves have undergone significant evolution in the direction of improving radiation safety. But if radiation technologies are constantly being improved, then approaches in the field of control and regulation of activities with ionizing radiation sources retain a high degree of conservatism. In this paper, the ways to improve the issues of regulation and regulation of activities in the use of ionizing radiation sources are substantiated. The purpose of the study is to conduct a radiation-hygienic assessment of working conditions in PET centers and develop proposals for improving regulatory requirements, taking into account the features of modern technologies.

Study of temperature annealing induced optical absorption and structural disorder in CaF2 single crystals irradiated with Xe132 heavy ions

2024-11-19T17:41:30+00:00

This article studies radiation processes in calcium fluoride (CaF₂) single crystals irradiated with 230 MeV Xe¹³² heavy ions. The study utilized absorption spectroscopy and thermal activation spectroscopy. The effect of thermal annealing on structural changes and optical absorption caused by radiation defects was studied. CaF₂ samples were subjected to step-by-step heating to temperatures from 295 K to 1023 K, which made it possible to trace the dynamics of crystal structure restoration and changes in optical characteristics. The experimental results on optical spectroscopy were analyzed in Tauc and Urbach coordinates. The results show that with increasing annealing temperature, the intensity of absorption bands decreases, indicating recombination of defect centers and a decrease in structural disorder. It was also revealed that at temperatures above 800 K, an increase in the Urbach energy and a shift in the fundamental absorption edge are associated with the formation of new structural defects. The work provides new data on the mechanisms of formation and evolution of radiation defects in ion-irradiated materials and opens up prospects for increasing the radiation resistance of CaF₂-based optical materials.

Biological protection of the flight crew of a nuclear-powered aircraft from ionizing radiation

2024-10-22T18:40:18+00:00

Intensive development of aircraft with nuclear engines (nuclear aircraft) was carried out from the mid-40s to the mid-60s of the twentieth century. The design bureaus of the leading nuclear powers of that period in nuclear-powered aircraft projects solved the main problem of long-range aircraft, which was limited supplies of traditional fuel, by using the high energy density of uranium-235, a few grams of which is enough to ensure flight continuity for tens of hours.The crew of an aircraft with a nuclear power plant and 2–4 nuclear turbojet engines located in the tail section could patrol the air non-stop for 2 weeks. Along with the obvious advantage in the form of extraordinary productivity of nuclear fuel, nuclear-powered aircraft had significant disadvantages, such as large dimensions and large mass of the reactor installation, catastrophic consequences of accidents and inevitable radioactive contamination of vast territories or water areas, as well as chronic exposure of the flight crew to radionuclide sources of ionizing radiation generated in the result of a chain reaction.If the problem with the mass-dimensional dimensions of a nuclear reactor for nuclear aircraft was solved at the Tupolev Design Bureau, and the safety of the reactor in the event of an accident was proposed to be ensured by separating it from the fuselage and subsequent soft landing on a parachute system, then the issue of reducing radiation doses to flight crews remained open. This article proposes a method for selecting a protective material and calculating its thickness necessary to ensure the radiation safety of nuclear aircraft pilots, projects of which today have again become relevant and promising.The proposed method for calculating the thickness of the protective shield differs from generally accepted methods in that it takes into account changes in the rules for determining calculated and standardized radiation doses in accordance with today's requirements of national and international legislation in the field of ensuring and monitoring the state of radiation safety.

Neutron diffraction studies of structures and phase transitions in ternary Fe-Ga-RE alloys (RE = Dy, Er, Pr, Sm, Tb, Yb)

2024-10-24T09:37:24+00:00

New data on the phase compositions and structural transformations in Fe₈₁Ga₁₉ and Fe₇₃Ga₂₇ alloys doped with trace amount (~0.1 − 0.5 at.%) of rare earth elements (RE) (Dy, Er, Pr, Sm, Tb, Yb) are presented. The structural data were obtained in neutron diffraction experiments performed with high resolution and in the continuous temperature scanning mode during heating to 900°C and subsequent cooling at a rate of ±2 °C/min. At a small amount of the RE element (≤ 0.2 at.%), structural rearrangements proceed in generally the same way both in the initial Fe₈₁Ga₁₉ and Fe₇₃Ga₂₇ alloys and in their alloyed analogs. On the contrary, in Fe₇₃Ga₂₇RE alloys with RE in the amount of ~0.5 at.%, both the sequence of forming and disappearing structural phases and the final state of the alloy depend on the type of rare earth element. In the initial (as-cast) state, the microstructure of Fe₈₁Ga₁₉RE alloys is predominantly a disordered matrix (phase A2) with regions of short-range order of the D0₃ type. The process of continuous slow heating leads to the formation of clusters of the ordered phase D0₃ with sizes in the range of (200 – 300) Å. The microstructure of most Fe₇₃Ga₂₇RE alloys with RE in the initial state is a structurally disordered matrix (phase A2) with dispersedly embedded clusters of the D0₃ phase with characteristic sizes of ~900 Å. During slow heating and cooling, a homogeneous state is formed in these alloys. The tetragonal phase L6₀, previously discovered in electron diffraction studies of surface layers of similar alloys, was not found in neutron diffraction spectra formed by the entire volume of samples in any of the studied Fe-Ga-RE alloys.

The equations of dispersion of TE and TM waves in a semi-closed plane waveguide of monoclinic anisotropy

2024-11-19T17:32:28+00:00

This article is devoted to the study of waveguide propagation of electromagnetic waves in a semi-closed flat layer of monoclinic anisotropy, in the coordinate plane (yz). The regularities of electromagnetic wave processes are important in many fields of engineering and scientific research. Traditionally, the propagation of optical range waves with the anisotropy of the permittivity tensor and the isotropy of the magnetic permeability tensor has been more studied [1-8].

The patterns of wave propagation in waveguides are used in the creation of devices and devices for various purposes Wave processes in waveguides have dispersion. The presence of dispersion allows you to control and form the necessary properties of wave processes in waveguides.

The patterns of wave dispersion are described by the dependence of the phase and group velocities of waves in waveguides on frequency. The solution of the dispersion equations determines this dependence. In this paper, the equations of dispersion of TE and TM polarization waves in a plane dielectric waveguide of monoclinic anisotropy are obtained. One boundary of the layer is metallized, the other is in contact with a semi-infinite medium. In the case of elastic waves of SH polarization, wave processes in semi-closed waveguides are called Love waves. One of the boundaries of the elastic layer is free, the other is in contact with a semi-infinite elastic medium. Love waves are considered in problems of seismology, geophysics, etc.

CALCULATION OF FORM FACTORS AND SEMI-LEPTON BRANCHINGS OF THE B → ρ TRANSITION IN THE COVARIANT QUARK MODEL

2024-10-28T06:19:56+00:00

In this paper, we study the transition in the framework of the covariant confined quark model. The covariant confined quark model is a quantum field approach to hadron interactions based on the Lagrangian of the interaction of hadrons interacting with their constituent quarks. An important difference from other theoretical models is that the numerical results (form factors, branchings, widths and angular observables) are calculated over the entire kinematic range of the transferred momentum . The transition is a subject of interest in high energy physics. Form factors and branchings have been obtained in different theoretical approaches. Experimentalists from the LHCb collaboration plan to measure this decay in the future, since this transition occurs with a changing flavor of neutral current. In this work we have calculated the form factors for the transition over the entire kinematic range of the transferred momentum . We have compared the numerical results from our model with the predictions of other theoretical approaches. We have converted our form factors into the Bauer-Stech-Wirbel (BSW) form factors for comparison with other theoretical approaches. The theoretical predictions are in satisfactory agreement with each other. Using these form factors we have calculated the branchings for the semileptonic decay , where are leptons. We have plotted the behavior of the form factors and branchings as functions of the squared momentum transfer. The results obtained in this work have demonstrated a high degree of agreement with the predictions of other theoretical models such as the light-cone sum rules, lattice quantum chromodynamics, and the relativistic quark model. This confirms the reliability and accuracy of the covariant confined quark model for studying rare decays involving heavy quarks.

Cathodoluminescence characteristics of bismuth-doped lanthanide niobates

2024-11-04T07:48:24+00:00

The study is devoted to the study of lanthanide niobates activated by bismuth, interesting in connection with the use of these materials in the production of phosphors used in various fields of human activity, medicine, industry, science. The purpose of the study is to study the luminescent characteristics of phosphors suitable for use in solid-state light sources and field emission displays. At present, the most thoroughly studied lanthanide niobates are lutetium, yttrium and gadolinium activated by various trivalent rare-earth ions (Eu³⁺, Tb³⁺, Dy³⁺). Much less studied are niobates activated only by Bi³⁺ ions or simultaneously by both Bi³⁺ ions and rare-earth ions. In the presented study, microcrystalline powders of yttrium, lutetium and gadolinium niobates doped with trivalent bismuth were studied by cathodoluminescence spectroscopy in a wide temperature range. The study was carried out under excitation by an electron beam with an energy of about 100 keV, having a penetration depth of more than 20 μm to reduce the influence of surface effects on luminescence. For the samples of (Y, Lu, Gd) NbO4: Bi, as well as nominally pure LuNbO₄, the cathodoluminescence spectra were measured, both integral and with time resolution. A comparison with the photoluminescence characteristics of these samples was carried out. An assumption was made that intense wide bands of cathodoluminescence have a complex structure and are a superposition of several bands of exciton nature. The presence of weak ultrafast radiation in the ultraviolet region of the spectrum related to the so-called intraband luminescence was noted. The obtained data are of both scientific and practical interest in the further development of functional materials.

HYBRID COMPOSITE MATRICES TO PREVENT RADIONUCLIDES FROM SPREADING INTO THE ENVIRONMENT

2024-11-26T09:32:51+00:00

The effective creation of hybrid composite materials (HCM) with significant sorption abilities for radionuclides in liquid radioactive waste has been discussed. These hybrid composite materials are made up of two sorbents, which are derived from an organic source and a natural mineral containing intercalated ferrocyanide complexes of transition metal ions. A substantial degree of radionuclide uptake is noted during the initial phase of sorption, which is linked to the plentiful active sites on the surfaces of the hybrid composition. In contrast, the subsequent stage of sorption shows diminished and slower radionuclide uptake, likely due to the gradual saturation of the remaining active sites within the HCM. Therefore, the rapid sorption can be associated with adsorption taking place on the outer surfaces of the materials, in contrast to the extended adsorption process observed in the macropores of the composite materials.

A thorough hydrodynamic-geochemical mathematical model was developed to represent the fixation and concentration mechanisms that clarify the movement of radionuclides through artificial geochemical barriers associated with liquid radioactive waste.

Study of resonance reactions at the DC-60 cyclotron using the TTIK and time-of-flight techniques

2024-11-25T18:56:45+00:00

The article is devoted to the review of the work done on the first successful implementation of the thick target method in inverse kinematics (TTIK) based on the DC-60 cyclotron. The use of the TTIK technique together with the time-of-flight system for heavy ion beam diagnostics and reaction product identification made it possible to study resonance nuclear reactions in the region of low interaction energies, which are also of astrophysical interest. The technique is based on measuring the excitation functions of light particle scattering under inverse kinematics conditions, where a thick and extended gas target (helium or hydrogen) is used as a target, and heavy accelerated nuclei serve as a beam. In addition, it provides a detailed description of the implemented experimental scheme and the data acquisition and processing systems. As a result, the overall experimental resolution of about 35 keV and 2 ns at an angle of 180° in the center of mass system (cms) was achieved. Moreover, the use of the TTIK method allowed us to eliminate background reactions by using ultra-pure light gases helium and hydrogen as a target and heavy particle isotope beams. All this together allowed our group to successfully conduct a series of experiments to study the resonance structure of ²⁰Ne, ²¹Ne, ¹⁹F, ²²Ne nuclei in the reactions ¹⁶O+α, ¹⁷O+α, ¹⁵N+α and ²²Ne+α, respectively.

Influence of Material Composition of Filters on Spatial-Energy Distribution of Neutrons at the Outlet of the Horizontal Experimental Channel of WWR-K Research Reactor

2024-11-18T04:38:55+00:00

Annotation. This paper investigates the effect of filters on the spatial-energy distribution of neutrons in the horizontal experimental channels of the WWR-K research reactor. The introduction presents an overview and the role of the reactor, the features of the horizontal channels and their importance for scientific research. The main types of filters, their purpose and key role in neutron spectrum control are described. The methodology of the work includes a description of the method used, including a description of the mathematical model. The material composition and properties of the considered filters are described. In the section ‘Results and Discussion’ the results of calculations on the spatial-energy distribution of neutrons at the outlet of the horizontal experimental channel of the WWR-K reactor without a filter and with different composition of filters are presented. The influence of each type of filter on the spectral characteristics of the neutron flux is analysed, the peculiarities of each filter and practical aspects of its application are given. The significance of the results obtained for further optimisation of radiation conditions of the WWR-K neutron beam is emphasised. In conclusion, a brief summary of the results and future plans for the continuation of research aimed at the formation of a therapeutic neutron beam at the WWR-K reactor are given.

Keywords: boron neutron capture therapy, research reactor, beam forming unit, epithermal spectrum, thermal spectrum.

Analysis of semileptonic decay widths of η(1295,1475) mesons

2024-10-15T13:28:46+00:00

The decays of excited and mesons with the production of vector mesons and a lepton pair and are investigated. It is shown that these decays are described by a contact diagram with direct production of a lepton pair by a photon field and a diagram with intermediate vector fields and . Theoretical estimates for the integral decay widths are obtained.The relative roles of the channels in determining the decay widths are investigated. It is shown that decays with the production of an electron-positron pair are mainly determined by the contribution of the diagram with contact interaction. Channels with vector mesons play a more important role in the decays of mesons with the production of a muon pair.The matrix elements corresponding to the quark loops with vertices and are calculated. Mesons and are considered as the first radially excited states of mesons and .The calculations are performed in the one-loop quark approximation in the leading order of the 1/Nс expansion. Predictions for a number of processes planned in future hadron factories are obtained. The results of theoretical calculations are important for understanding the structure of mesons and their interaction with hadron and lepton fields. The obtained decay data can be used in future meson factories.The implementation of such a hadron factory is planned at the Fermilab proton beam where the number of events is expected to be at the level of for the – meson which is several orders of magnitude higher than current experiments. Another meson factory will be built at the HIAF heavy ion accelerator in China.

Synthesis and optical property of the high entropy compounds Y2,69-хCa0,3Li0,01(Eu or Ce)хAl5O12

2024-10-24T10:05:27+00:00

The results of powder X-ray diffraction analysis (XRD)of compounds with a new high entropyY_2,69-хCa_0,3Li_0,01(EuorCe)_хAl₅O₁₂garnet crystal structure synthesized by the sol-gel method showed that it is a single-phase cubic structure. According to the results of the XRD analysis of monocrystalline compounds of the garnet structure, the garnet phase is defined as the main crystalline phase with an increase in the amount of Ca²⁺, Li+ and Eu³⁺, Ce³⁺ ions. The results of the X-ray diffraction analyzes of the synthesized samples are fully confirmed by the infrared (FT-IR) spectroscopic data. In the region of 1000–400 cm⁻¹ of the FT-IR spectra, the intense peaks characteristic of garnets appeared the same for all samples. Several intense peaks distributed in the region of 1000–400 cm⁻¹ of garnets describe the mode of stretching of tetrahedral units. The surface morphology of high-entropy garnets obtained by scanning electron microscopy (SEM) was very similar for all samples, and the bulk grains consisted of spherical particles with an average size of about 50–120 nm. The calculated cell parameters were in the range of 12.316 12.322 nm without any process at the substitution level, which confirms the formation of high-entropy garnet materials. The exact chemical composition of garnet structural compounds with various additives was determined by the ICP-OES method. According to the excitation and emission spectra, the sol-gel method is effective for the preparation of compounds with a high-entropy garnet crystal structure, and they can be used as a matrix for creating new phosphors.

Study of elastic properties of Na2SO4-V crystal by DFT method

2024-11-06T07:42:45+00:00

This paper studies the elastic properties of doped Na₂SO₄ crystal using the density functional theory (DFT) method with the HSE06 hybrid functional. The work aims to understand the mechanical characteristics of Na₂SO₄ at different pressures in order to develop more efficient thermoluminescent dosimeters (TLDs). The results show that at pressures up to 15 GPa, a number of structural changes occur that affect the plasticity and elasticity of the material. An important achievement was the identification of critical points at which the crystal changes its behavior: the transition from a plastic to a brittle state occurs at a pressure of about 12 GPa. The paper details the mechanisms governing the deformation of the crystal under pressure and discusses the possibility of phase transitions. These findings have important implications for the future use of Na₂SO₄ in radiation dosimetry and other applications where the material's resistance to mechanical stress is critical.

Recombination emission in the phosphor CaSO4-Pb2+

2024-10-22T18:30:19+00:00

Optical methods were used to investigate the formation of combined or induced electronic emissive states in irradiated CaSO₄-Pb²⁺ phosphor at 2.9 eV and 3.1 eV. The combined electronic emissive state consists of electronic states of impurity Pb+-SO₄^- and intrinsic SO₄^3--SO₄^- trapping centers. The impurity electronic states are formed by capturing free electrons of conduction band by Pb²⁺ impurities and localizing electrons resulting from charge transfer from the excited anion complex SO₄^2-(O^2--Pb²⁺) impurities by reaction Pb²⁺+(e^-+SO₄^-)→Pb⁺-SO₄^-. The intrinsic electronic states are formed by capturing free electrons of conduction band by anion complexes or by localizing electrons resulting from charge transfer from the excited anion complex SO₄^-(O^2--SO₄^2-) to neighboring anion complexes by reaction SO₄^2-+(e^-+SO₄^-)→SO₄^3--SO₄^-. The combined electronic emissive states at 2.9 eV and 3.1 eV are excited by photons of 3.9-4.0 eV and 4.5 eV. It was also experimentally shown that in the phosphor with induced trapping centers, recombination emissions at 3.1 eV and 2.9 eV are regenerated upon excitation by photons of 3.9-4.0 eV and 4.5 eV. Thus, energies of 3.9-4.0 eV and 4.5 eV are the excitation and absorption energies between the electronic and hole trapping centers located in the transparency region of CaSO₄-Pb²⁺phosphor.