Physics of Atomic Nuclei最新文献

IH (Interdigital H-type) and SPR (split ring) structures are used to accelerate ions at low energies and relatively low operating frequencies. A procedure for selecting the parameters of drift tubes (DTs) is proposed to achieve high HF efficiency and simultaneously suppress the dipole parasitic component of electric fields at a given electrical strength. A database of DT variants based on six free geometric parameters is compiled using modern software in an electrostatic 3D approximation. The final variant is selected through sequential interpolation of the database. Fourier coefficients of the expansion of the accelerating field on its axis are also derived to calculate the particle dynamics in the selected DT variants.

Plastic scintillators based on polystyrene and other polymers of the vinyl aromatic series (polyvinyltoluene, polyvinylxylene, etc.) have long been used in scintillation detectors because of their short fluorescence lifetimes, low cost, and relative ease of fabrication. On the other hand, these materials have a small light output. Plastic scintillators are usually doped with fluorescent organic dyes to impart scintillation properties to the polymer matrix and increase the light yield. In recent years, considerable interest has been aroused by studies aimed at the use of semiconductor nanocrystals (quantum dots) as dopants for plastic scintillators based on polymer matrices. The most promising materials for this purpose are considered to be CsPbBr₃ perovskite nanocrystals and CdSe/ZnS quantum dots of the core/shell type. These materials have high quantum yields, and high effective atomic numbers and can be effectively integrated into polymer matrices while preserving their structural and optical properties. Thus, it can be hypothesized that doping plastic scintillators with quantum dots can significantly improve their light yield and increase their radiation resistance. Here, we propose an approach to the chemical design of plastic scintillators doped with quantum dots, investigate their radioluminescence, and describe the optimal parameters for the fabrication of such composite scintillators by radical polymerization of para-methylstyrene.

In the paper, the results of studies of processes during fast output energy regulation of a linear accelerator for proton-beam therapy during one RF pulse have been summarized. Both the features of the formation of the required RF power pulse and the propagation of the RF pulse in an inertialess dispersed structure on a traveling wave have been considered. Particular attention has been paid to the dynamics of particles in a nonstationary electromagnetic RF field. The use of the considered regulation method will allow a multiple increase in the scanning speed along the depth of the irradiated object.

Results are presented from studying physicochemical characteristics and radiosensitizing properties of a new type of lutetium fluoride (LuF₃) nanoparticle as a promising nanoradiosensitizer for X-ray irradiation of B16/F10 melanoma cells. A comprehensive analysis is performed of functional characteristics of synthesized LuF₃ nanoparticles, their cytotoxicity, and their radiosensitizing effect in vitro. It is shown that LuF₃ nanoparticles have a hydrodynamic diameter of less than 200 nm. Colloidal sol obtained on their basis is highly stable as a result of using the biocompatible stabilizer ammonium citrate. LuF₃ nanoparticles have a cytotoxic and radiosensitizing effect on melanoma cells in concentrations of 116 mg/mL and higher by reducing their metabolic activity and membrane mitochondrial potential while initiating apoptosis. Such nanomaterial can form the basis of promising modern approaches to increasing the effectiveness of radiation therapy.

Hafnium hydride is studied as an absorber for fast neutron reactors. A high value of the neutron absorption cross section is noted that is retained by all hafnium isotopes formed during neutron irradiation in reactor. However, there is a risk of hafnium hydride decomposing in the range of 600–700°C, which corresponds to the operating temperature of absorbers in fast neutron reactors. An approach is proposed to reduce hydrogen evolution from hafnium hydride that consists of applying a protective hafnium oxide coating to it. Hafnium hydride samples are annealed in helium at temperatures of 1200°C in a synchronic thermal analysis setup. Hydrogen desorption starts at a temperature of 640°C. Complete hydrogen evolution is observed at a temperature of 1200°C. A substantial drop in hydrogen evolution at low temperatures is seen when annealing samples with applied coatings. A special setup is developed that allows the thermal testing of hydride materials in a liquid sodium environment. Hafnium hydride is annealed in liquid sodium at 700°C. Synchronic thermal analysis of samples after exposure to sodium reveals a drop in the emission of gas that is associated with an increase in the thickness of the oxide layers on the surfaces of samples.

The current–voltage characteristics of a superconducting disk with the Corbino current supply at an external static magnetic field of 1000 Oe have been calculated within the two-dimensional model of a layered high-temperature superconductor. The field strength on several coaxial rings of the sample has been obtained and the critical currents for three values of the diameters, temperatures, and densities of defects have been evaluated. The effect of the concentration of point defects and temperature on the velocity of Abrikosov vortices has been studied.

A multiscale study of the structure of spherical particles (granules) of rapidly quenched powder of a heat-resistant (α + β) titanium-based alloy obtained by the PREP method, which has been subsequently used for the manufacture of products using PM HIP technology, has been carried out. Metallography LM, SEM, EDX, OIM methods are used to study the structure of granules of different sizes. The influence of the granule size and vacuum heat treatment at temperatures in the fields of the (α + β) and β phases on the regularities of the formation of the microstructure of granules has been revealed. The dendrite microstructure of grains of the metastable β phase has been found in the particles (granules) of the original rapidly quenched PREP powder. Dendrite segregation of alloying elements is clearly revealed in larger particles, for example, for Mo. In smaller particles, the formation of a more highly dispersed structure has been observed. The effect of granule size decreasing on the reduction of the size parameter of the dendritic structure (SDAS) has been determined. Schematic TTT diagrams of phase transformations in the studied alloy, including crystallization, martensitic transformation, and normal diffusion transformation β → (α + β), have been constructed.

A condition for the most optimal characteristics of the accumulator is obtained by using a quasi-stationary one-dimensional model of heat transfer in flow heat accumulators. The concept of the efficiency coefficient of recuperative heat exchangers for estimating the phase transition accumulator is substantiated. Approaches of physical and mathematical modeling to obtain analytical relations used to calculate heat transfer processes in flow accumulators with phase transitions, characterized by the uneven temperature field in the direction of the coolant flow, are analyzed. The dependences obtained are applicable to calculate the initial and final stages of the phase transition process. The application of the dependences obtained for more accurate calculations is justified.

The Atomic Reactor Research Institute is developing the design of an irradiator for conducting in-reactor tests of neutron-absorbing materials in nuclear reactor control systems. Dysprosium titanate is chosen as the absorbing material due to its high chemical and thermal stability, along with its enhanced corrosion and radiation resistance. The irradiator’s design consists of a suspension with a flange, a working section where the sample with the absorbing material is placed, a flow separator, and an absorbing screen. The flow separator is made of 12Kh18N10T stainless steel. The absorbing screen, designed to reduce the proportion of thermal neutrons in the spectrum, consists of two cylinders made of boron steel and aluminum, encased in 12Kh18N10T stainless steel. Neutron-physical calculations are made using the MCU-FR code, in addition to thermal-hydraulic calculations of the RD design obtained using the SolidWorks software. The calculations show that using a screen made of boron steel and aluminum allows the ratio of fast and thermal neutron flux to be adjusted during in-reactor tests of the absorbing materials. Results from thermal-hydraulic calculations show that using high-temperature loop installation VP-3 of the SM-3 reactor under conditions of forced circulation ensures the required temperature regime for irradiating a sample with dysprosium titanate in the third row of the SM-3 reflector.

In this work, a multipoint kinetics model for a VVER-1200 nuclear reactor consisting of a diverse (two-point, four-point, six-point, eight-point, and ten-point) set of point kinetics models in the axial direction that are coupled to each other by coefficients determined in the diffusion approximation is proposed and simulated in MATLAB environment. For a more precise description of the dynamic modes of the reactor, the model is provided with power reactivity feedback determined by temperature effects of reactivity and Mann’s approach to describing thermal-hydraulic processes in which it is assumed that two coolant nodes are adjacent to a single fuel node. The effect of different numbers of delayed neutron groups on the accuracy and speed of simulation of transient processes in the load-following mode is tested on the model with four axial points. In addition, a new mathematical model of control rods (CRs) is proposed that uses a combination of sign functions to sequentially influence all nodes during insertion or withdrawal. The results of numerical simulation show that the statistical accuracy of the proposed model is satisfactory, and general assumptions about transients are consistent with their physical definitions. This research contributes to the advancement of point nuclear reactor models for improving the synthesis of an automatic power controller.