The development of effective focusing schemes for positron bunches in plasma accelerators remains a significant challenge, as nonlinear regimes fail to create stable focusing channels for positrons. This work presents a method for focusing and improving the quality of positron bunches using a plasma lens operating in the linear regime. Through numerical simulations, we investigate two distinct focused positron bunch profiles: a purely Gaussian bunch and an elongated, flat-top bunch with Gaussian rising and falling edges. For both configurations, the results demonstrate the capability to achieve high-quality transverse focusing. Furthermore, beyond focusing, the proposed system enables potential possibility to reduce energy spread of positron bunches of the sequence after precursor.

The theory of first-order processes in the fine structure constant involving a polarized virtual (intermediate) photon state in the field of a linearly polarized electromagnetic wave has been developed. The obtained results constitute a part of the theory of second-order processes with respect to the fine-structure constant, whose probabilities can be expressed in terms of the probabilities of first-order processes.

An experimental study of the parameters of electromagnetic and X-ray radiation was carried out on a small-sized direct-acting electron accelerator with inductive storage and a plasma opening switch. Frequency spectra have been determined, and the diagnostics of the power of the microwave component of the spectrum has been tested. An analytical comparison of radiation signals and power signals has been carried out. A method for determining the directivity pattern using a broadband power sensor has been proposed. An anechoic chamber and a reflective screen were used to suppress interference.

For the reaction 12C(γ,np) 10B, a kinematic model was developed assuming a sequential two-particle decay with the formation of an intermediate excited nucleus. The possibility of decay through two channels - (n+11C*) or (p+11B*) - was created. In the system of the center of mass of a two-particle reaction, the kinematics is determined by the fact that, regardless of the specific type of interaction, the reaction products scatter at an angle of 180 and have equal modulus momentum, and their energies in the same system depend only on the masses of the particles and the total energy of the system. To visualize model calculations in the Python programming language, a graphical application was created with the possibility to interact with experimental data on the 12C(γ,np) 10B reaction. Comparison of kinematic calculations with experimental results allowed us to identify certain limitations for the selection of experimental events corresponding to the channel of sequential two-particle decay.

A comprehensive theoretical analysis of reactions of protons with an energy of 50 MeV on nuclei 12C, 14N, and 16O was performed using the TALYS-1.96 code. The calculated cross-sections are compared with fundamental experimental data obtained by the photoemulsion method. It has been established that standard statistical models (Hauser-Feshbach) and pre-equilibrium models in TALYS satisfactorily describe a number of channels, in particular 16O(p, pn)15N. At the same time, calculations quantitatively confirm that channels with neutron emission, not taken into account in [1], constitute 39…46% of the total inelastic cross-section, which explains ≈ 40% of unidentified events in the original experiment [1]. Analysis of intermediate resonances shows that the cross-sections of formation 8Be and 9B are significant (up to 71 mb), confirming their dominant role in cascade decays. A key finding is the critical discrepancy for the channel 16O(p, p4α): the experimental cross-section (78.1 mb) [1] cannot be explained by statistical models (TALYS prediction gives < 17 mb) [5], indicating the dominance of direct cluster mechanisms of the reaction.

The results of systematic experimental studies of the yield of δ-electrons during the interaction of an electron beam with energies of 10, 15, and 25 MeV with thin amorphous targets (Be, Al, Ni, Cu, Nb, Au) are presented. The studies were carried out in 2025 at the LPE-30 accelerator of the National Scientific Centre of “Kharkiv Institute of Physics and Technology” using a multi-target device. The key feature of the experiment was the unique selection of the target thickness, which provided close values of the parameter T0.5Z/A (in the range of 0.045…0.065), characterizing the collision statistics normalized to the specific electron density of the target. Thus, the thickness T for each target (with different Z/A ratios) was selected so that the total statistical effect of the interaction with electrons of the substance was close for all targets. It was found that under such conditions, the yield of δ-electrons weakly depends on the energy in the range of 10…25 MeV and is practically independent of the target serial number Z (deviation within 5…10%). This demonstrates that under the same beam scattering conditions, the yield of δ-electrons is determined mainly not by the type of material (Z), but by the сollision statistics (thickness). A semi-automated measurement system based on the ADS1115 ADC and Arduino Nano has been developed and implemented for measuring the current-voltage characteristics of secondary emission.

The effect of the endogenous titanium nitride inclusions on local stresses in the matrix of 08Kh18N10T austenitic steel was studied. For spherical inclusions coherent with the matrix, local stresses were obtained. Local stresses exceeded the minimum yield strength. The trend in stress variation with inclusion size and shape was determined. It has been demonstrated that the magnitude of stresses escalates with the enlargement of TiN inclusion size and the transition of their morphology from spherical to cubic forms. Additionally, the characteristics of matrix failure in the vicinity of clusters of endogenous TiN inclusions are analyzed.

This paper presents the results of an FTIR spectroscopy study on the physical and chemical structural modifications induced by gamma irradiation in HDPE polymer and HDPE/GaAs<Te> composite films in absorbed dose range of Фγ = 50…350 kGy. It has been shown that gamma irradiation causes changes in the degree of crystallinity and the formation of polyene (–C=C–) and carbonyl (C=O) groups in polymer and composite films. The dose dependencies for these modifications exhibit a similar trend, indicating a direct relationship between the degree of crystallinity and the crosslinking process. Comparative analysis confirms that composite films are more radiation resistant than the polymer films.

This study proposes a method for calculating the field emission parameters using two linear regions of FowlerNordheim plots. The method allows to get the values of the work function, field enhancement factor and area efficiency of emission. Based on this method, an analysis of the emission properties of titanium nitride synthesized using reactive Arc-PVD was carried out. The calculated work function values are in good agreement with the values reported in other studies. The obtained relationships between the field enhancement factor and area efficiency of emission for materials with the same composition can be explained by the features of the surface morphology.

This review presents the main results on the synthesis and study of quasicrystalline samples of the Ti-Zr-Ni system. The research was conducted over a number of years in Kharkiv by a team of researchers from the National Science Center “Kharkiv Institute of Physics and Technology”, Kharkiv State University named after V.N. Karazin and NTU KhPI and was headed by the outstanding scientist, academician V.M. Azhazha. Many of the results obtained became priorities. Such research became possible thanks to the experience and developments of the current Department of Pure Metals, Metal Physics and Technology of New Materials at NSC KIPT. The results of fruitful cooperation between the teams are reflected in this review. It is dedicated to the bright memory of Academician Vladimir Mikhailovich Azhazha, as well as Prof. Merisov B.A., Prof. Pugachov A.T. and Dr. Lavrinenko S.D.